From be5dd5eea7389b5ccfa8fbb95f9f3c62b44c390c Mon Sep 17 00:00:00 2001
From: Illia Sheremetov <i.sheremetov@cksource.com>
Date: Tue, 1 Aug 2023 17:44:26 +0200
Subject: [PATCH 01/16] Fix (engine): detecting restricted objects in firefox

---
 .../src/view/observer/selectionobserver.ts    | 22 ++++++++++
 .../tests/view/observer/selectionobserver.js  | 40 +++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts b/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts
index b31a1ab2abd..d10b0e3513a 100644
--- a/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts
+++ b/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts
@@ -232,6 +232,10 @@ export default class SelectionObserver extends Observer {
 
 		const domSelection = domDocument.defaultView!.getSelection()!;
 
+		if ( env.isGecko && this._isObjectRestricted( domSelection.getRangeAt( 0 ).startContainer ) ) {
+			return;
+		}
+
 		if ( this.checkShouldIgnoreEventFromTarget( domSelection.anchorNode! ) ) {
 			return;
 		}
@@ -302,6 +306,24 @@ export default class SelectionObserver extends Observer {
 		}
 	}
 
+	// In firefox exists restricted objects. Trying get any property from restricted object, it will through an error.
+	// https://github.com/ckeditor/ckeditor5/issues/9635
+	private _isObjectRestricted( obj: unknown ): boolean {
+		let isRestricted;
+
+		try {
+			if ( Object.prototype.toString.call( obj ) ) {
+				isRestricted = false;
+			} else {
+				isRestricted = true;
+			}
+		} catch ( error ) {
+			isRestricted = true;
+		}
+
+		return isRestricted;
+	}
+
 	/**
 	 * Clears `SelectionObserver` internal properties connected with preventing infinite loop.
 	 */
diff --git a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
index 32032666d5f..bcbf7400849 100644
--- a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
+++ b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
@@ -162,6 +162,46 @@ describe( 'SelectionObserver', () => {
 		changeDomSelection();
 	} );
 
+	it( 'should not pass non-valid object in firefox', done => {
+		testUtils.sinon.stub( env, 'isGecko' ).value( true );
+		testUtils.sinon.stub( Object.prototype, 'toString' ).value( () => null );
+
+		const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );
+
+		changeDomSelection();
+		setTimeout( () => {
+			sinon.assert.notCalled( spy );
+			done();
+		}, 100 );
+	} );
+
+	it( 'should detect restricted object in firefox', done => {
+		testUtils.sinon.stub( env, 'isGecko' ).value( true );
+		testUtils.sinon.stub( Object.prototype, 'toString' ).throws(
+			new Error( 'Permission denied to access property Symbol.toStringTag' )
+		);
+
+		const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );
+
+		changeDomSelection();
+		setTimeout( () => {
+			sinon.assert.notCalled( spy );
+			done();
+		}, 100 );
+	} );
+
+	it( 'should pass valid object in firefox', done => {
+		testUtils.sinon.stub( env, 'isGecko' ).value( true );
+
+		const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );
+
+		changeDomSelection();
+		setTimeout( () => {
+			sinon.assert.calledOnce( spy );
+			done();
+		}, 100 );
+	} );
+
 	it( 'should add only one #selectionChange listener to one document', done => {
 		// Add second roots to ensure that listener is added once.
 		createViewRoot( viewDocument, 'div', 'additional' );

From ea2baf9183de2bfcb2ca6f1bc6cefe8530b635d5 Mon Sep 17 00:00:00 2001
From: Illia Sheremetov <i.sheremetov@cksource.com>
Date: Tue, 1 Aug 2023 17:48:26 +0200
Subject: [PATCH 02/16] Test (engine): typo fix

---
 .../tests/view/observer/selectionobserver.js                | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
index bcbf7400849..086e0cf8762 100644
--- a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
+++ b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
@@ -162,7 +162,7 @@ describe( 'SelectionObserver', () => {
 		changeDomSelection();
 	} );
 
-	it( 'should not pass non-valid object in firefox', done => {
+	it( 'should not pass non-valid object on Firefox', done => {
 		testUtils.sinon.stub( env, 'isGecko' ).value( true );
 		testUtils.sinon.stub( Object.prototype, 'toString' ).value( () => null );
 
@@ -175,7 +175,7 @@ describe( 'SelectionObserver', () => {
 		}, 100 );
 	} );
 
-	it( 'should detect restricted object in firefox', done => {
+	it( 'should detect restricted object on Firefox', done => {
 		testUtils.sinon.stub( env, 'isGecko' ).value( true );
 		testUtils.sinon.stub( Object.prototype, 'toString' ).throws(
 			new Error( 'Permission denied to access property Symbol.toStringTag' )
@@ -190,7 +190,7 @@ describe( 'SelectionObserver', () => {
 		}, 100 );
 	} );
 
-	it( 'should pass valid object in firefox', done => {
+	it( 'should pass valid object on Firefox', done => {
 		testUtils.sinon.stub( env, 'isGecko' ).value( true );
 
 		const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );

From 74d5f6dff926aadf165066a5d14ef128d5f0b5df Mon Sep 17 00:00:00 2001
From: Illia Sheremetov <i.sheremetov@cksource.com>
Date: Wed, 2 Aug 2023 12:06:09 +0200
Subject: [PATCH 03/16] Fix (engine): code review fixes

---
 .../src/view/observer/selectionobserver.ts    | 39 ++++++-------
 .../tests/view/observer/selectionobserver.js  | 55 ++++++++-----------
 2 files changed, 42 insertions(+), 52 deletions(-)

diff --git a/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts b/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts
index d10b0e3513a..8f670f5bdb4 100644
--- a/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts
+++ b/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts
@@ -232,7 +232,7 @@ export default class SelectionObserver extends Observer {
 
 		const domSelection = domDocument.defaultView!.getSelection()!;
 
-		if ( env.isGecko && this._isObjectRestricted( domSelection.getRangeAt( 0 ).startContainer ) ) {
+		if ( isRestricted( domSelection ) ) {
 			return;
 		}
 
@@ -306,24 +306,6 @@ export default class SelectionObserver extends Observer {
 		}
 	}
 
-	// In firefox exists restricted objects. Trying get any property from restricted object, it will through an error.
-	// https://github.com/ckeditor/ckeditor5/issues/9635
-	private _isObjectRestricted( obj: unknown ): boolean {
-		let isRestricted;
-
-		try {
-			if ( Object.prototype.toString.call( obj ) ) {
-				isRestricted = false;
-			} else {
-				isRestricted = true;
-			}
-		} catch ( error ) {
-			isRestricted = true;
-		}
-
-		return isRestricted;
-	}
-
 	/**
 	 * Clears `SelectionObserver` internal properties connected with preventing infinite loop.
 	 */
@@ -353,6 +335,25 @@ export type ViewDocumentSelectionEventData = {
 	domSelection: DomSelection | null;
 };
 
+// In firefox exists restricted objects. Trying get any property from restricted object, it will through an error.
+// https://github.com/ckeditor/ckeditor5/issues/9635
+function isRestricted( domSelection: DomSelection ): boolean {
+	if ( !env.isGecko ) {
+		return false;
+	}
+
+	let isRestricted = false;
+
+	try {
+		const container = domSelection.getRangeAt( 0 ).startContainer;
+		Object.prototype.toString.call( container );
+	} catch ( error ) {
+		isRestricted = true;
+	}
+
+	return isRestricted;
+}
+
 /**
  * Fired when a selection has changed. This event is fired only when the selection change was the only change that happened
  * in the document, and the old selection is different then the new selection.
diff --git a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
index 086e0cf8762..2667c24ffc5 100644
--- a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
+++ b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
@@ -162,44 +162,33 @@ describe( 'SelectionObserver', () => {
 		changeDomSelection();
 	} );
 
-	it( 'should not pass non-valid object on Firefox', done => {
-		testUtils.sinon.stub( env, 'isGecko' ).value( true );
-		testUtils.sinon.stub( Object.prototype, 'toString' ).value( () => null );
+	describe( 'Restricted objects handling in Gecko', () => {
+		it( 'should detect restricted object on Firefox', done => {
+			testUtils.sinon.stub( env, 'isGecko' ).value( true );
+			testUtils.sinon.stub( Object.prototype, 'toString' ).throws(
+				new Error( 'Permission denied to access property Symbol.toStringTag' )
+			);
 
-		const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );
+			const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );
 
-		changeDomSelection();
-		setTimeout( () => {
-			sinon.assert.notCalled( spy );
-			done();
-		}, 100 );
-	} );
-
-	it( 'should detect restricted object on Firefox', done => {
-		testUtils.sinon.stub( env, 'isGecko' ).value( true );
-		testUtils.sinon.stub( Object.prototype, 'toString' ).throws(
-			new Error( 'Permission denied to access property Symbol.toStringTag' )
-		);
-
-		const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );
-
-		changeDomSelection();
-		setTimeout( () => {
-			sinon.assert.notCalled( spy );
-			done();
-		}, 100 );
-	} );
+			changeDomSelection();
+			setTimeout( () => {
+				sinon.assert.notCalled( spy );
+				done();
+			}, 100 );
+		} );
 
-	it( 'should pass valid object on Firefox', done => {
-		testUtils.sinon.stub( env, 'isGecko' ).value( true );
+		it( 'should pass valid object on Firefox', done => {
+			testUtils.sinon.stub( env, 'isGecko' ).value( true );
 
-		const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );
+			const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );
 
-		changeDomSelection();
-		setTimeout( () => {
-			sinon.assert.calledOnce( spy );
-			done();
-		}, 100 );
+			changeDomSelection();
+			setTimeout( () => {
+				sinon.assert.calledOnce( spy );
+				done();
+			}, 100 );
+		} );
 	} );
 
 	it( 'should add only one #selectionChange listener to one document', done => {

From 6060d9e39a027bccff2356053ac27f52211b871a Mon Sep 17 00:00:00 2001
From: Aleksander Nowodzinski <a.nowodzinski@cksource.com>
Date: Wed, 2 Aug 2023 16:48:57 +0200
Subject: [PATCH 04/16] Code refactoring.

---
 .../src/view/observer/selectionobserver.ts    | 39 +++++++++----------
 1 file changed, 19 insertions(+), 20 deletions(-)

diff --git a/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts b/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts
index 8f670f5bdb4..86e1b6b723a 100644
--- a/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts
+++ b/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts
@@ -232,7 +232,7 @@ export default class SelectionObserver extends Observer {
 
 		const domSelection = domDocument.defaultView!.getSelection()!;
 
-		if ( isRestricted( domSelection ) ) {
+		if ( isGeckoRestrictedDomSelection( domSelection ) ) {
 			return;
 		}
 
@@ -335,25 +335,6 @@ export type ViewDocumentSelectionEventData = {
 	domSelection: DomSelection | null;
 };
 
-// In firefox exists restricted objects. Trying get any property from restricted object, it will through an error.
-// https://github.com/ckeditor/ckeditor5/issues/9635
-function isRestricted( domSelection: DomSelection ): boolean {
-	if ( !env.isGecko ) {
-		return false;
-	}
-
-	let isRestricted = false;
-
-	try {
-		const container = domSelection.getRangeAt( 0 ).startContainer;
-		Object.prototype.toString.call( container );
-	} catch ( error ) {
-		isRestricted = true;
-	}
-
-	return isRestricted;
-}
-
 /**
  * Fired when a selection has changed. This event is fired only when the selection change was the only change that happened
  * in the document, and the old selection is different then the new selection.
@@ -386,3 +367,21 @@ export type ViewDocumentSelectionChangeDoneEvent = {
 	name: 'selectionChangeDone';
 	args: [ ViewDocumentSelectionEventData ];
 };
+
+// I certain cases, Firefox mysteriously assigns so called "restricted objects" to native DOM Range properties.
+// Any attempt at accessing restricted object's properties causes errors.
+// https://github.com/ckeditor/ckeditor5/issues/9635
+function isGeckoRestrictedDomSelection( domSelection: DomSelection ): boolean {
+	if ( !env.isGecko ) {
+		return false;
+	}
+
+	try {
+		const container = domSelection.getRangeAt( 0 ).startContainer;
+		Object.prototype.toString.call( container );
+	} catch ( error ) {
+		return true;
+	}
+
+	return false;
+}

From 141942795555ef4d132ea3e5d09cbc6ef18cad84 Mon Sep 17 00:00:00 2001
From: Aleksander Nowodzinski <a.nowodzinski@cksource.com>
Date: Wed, 2 Aug 2023 16:49:59 +0200
Subject: [PATCH 05/16] Tests: improvements to tests descriptions.

---
 .../tests/view/observer/selectionobserver.js                | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
index 2667c24ffc5..c19d44fedd0 100644
--- a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
+++ b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
@@ -163,7 +163,7 @@ describe( 'SelectionObserver', () => {
 	} );
 
 	describe( 'Restricted objects handling in Gecko', () => {
-		it( 'should detect restricted object on Firefox', done => {
+		it( 'should detect "restricted objects" in Firefox DOM ranges and prevent an error being thrown', done => {
 			testUtils.sinon.stub( env, 'isGecko' ).value( true );
 			testUtils.sinon.stub( Object.prototype, 'toString' ).throws(
 				new Error( 'Permission denied to access property Symbol.toStringTag' )
@@ -172,18 +172,20 @@ describe( 'SelectionObserver', () => {
 			const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );
 
 			changeDomSelection();
+
 			setTimeout( () => {
 				sinon.assert.notCalled( spy );
 				done();
 			}, 100 );
 		} );
 
-		it( 'should pass valid object on Firefox', done => {
+		it( 'should do nothing in Firefox if the DOM selection is correct', done => {
 			testUtils.sinon.stub( env, 'isGecko' ).value( true );
 
 			const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );
 
 			changeDomSelection();
+
 			setTimeout( () => {
 				sinon.assert.calledOnce( spy );
 				done();

From df10cb7c0e25214912c751dbc80c9318a5fc9e01 Mon Sep 17 00:00:00 2001
From: Aleksander Nowodzinski <a.nowodzinski@cksource.com>
Date: Wed, 2 Aug 2023 17:00:40 +0200
Subject: [PATCH 06/16] Tests: Made the restricted object test more specific.

---
 .../tests/view/observer/selectionobserver.js  | 39 +++++++++----------
 1 file changed, 18 insertions(+), 21 deletions(-)

diff --git a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
index c19d44fedd0..0e3e22efba8 100644
--- a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
+++ b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
@@ -3,7 +3,7 @@
  * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
  */
 
-/* globals setTimeout, document, console, Event */
+/* globals setTimeout, document, console, Event, Selection */
 
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 
@@ -163,33 +163,30 @@ describe( 'SelectionObserver', () => {
 	} );
 
 	describe( 'Restricted objects handling in Gecko', () => {
-		it( 'should detect "restricted objects" in Firefox DOM ranges and prevent an error being thrown', done => {
+		beforeEach( () => {
 			testUtils.sinon.stub( env, 'isGecko' ).value( true );
-			testUtils.sinon.stub( Object.prototype, 'toString' ).throws(
-				new Error( 'Permission denied to access property Symbol.toStringTag' )
-			);
+		} );
 
-			const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );
+		it( 'should detect "restricted objects" in Firefox DOM ranges and prevent an error being thrown', done => {
+			const domRangeStubWithRestrictedObject = domDocument.createRange();
 
-			changeDomSelection();
+			sinon.stub( domRangeStubWithRestrictedObject, 'startContainer' ).get( () => {
+				throw new Error( 'Permission denied to access property Symbol.toStringTag' );
+			} );
 
-			setTimeout( () => {
-				sinon.assert.notCalled( spy );
-				done();
-			}, 100 );
+			testUtils.sinon.stub( Selection.prototype, 'getRangeAt' ).returns( domRangeStubWithRestrictedObject );
+
+			expect( () => {
+				changeDomSelection();
+				setTimeout( done, 100 );
+			} ).to.not.throw();
 		} );
 
 		it( 'should do nothing in Firefox if the DOM selection is correct', done => {
-			testUtils.sinon.stub( env, 'isGecko' ).value( true );
-
-			const spy = sinon.spy( selectionObserver.mutationObserver, 'flush' );
-
-			changeDomSelection();
-
-			setTimeout( () => {
-				sinon.assert.calledOnce( spy );
-				done();
-			}, 100 );
+			expect( () => {
+				changeDomSelection();
+				setTimeout( done, 100 );
+			} ).to.not.throw();
 		} );
 	} );
 

From 6a5460622c2260051800d89365cb90260b4b0652 Mon Sep 17 00:00:00 2001
From: Illia Sheremetov <i.sheremetov@cksource.com>
Date: Thu, 3 Aug 2023 13:03:55 +0200
Subject: [PATCH 07/16] Fix (engine): moving implementation to domconverter

---
 .../ckeditor5-engine/src/view/domconverter.ts | 25 ++++++++++++++++++-
 .../src/view/observer/selectionobserver.ts    | 22 ----------------
 2 files changed, 24 insertions(+), 23 deletions(-)

diff --git a/packages/ckeditor5-engine/src/view/domconverter.ts b/packages/ckeditor5-engine/src/view/domconverter.ts
index d7c0ae8357a..2a0791a8372 100644
--- a/packages/ckeditor5-engine/src/view/domconverter.ts
+++ b/packages/ckeditor5-engine/src/view/domconverter.ts
@@ -31,7 +31,8 @@ import {
 	isText,
 	isComment,
 	isValidAttributeName,
-	first
+	first,
+	env
 } from '@ckeditor/ckeditor5-utils';
 
 import type ViewNode from './node';
@@ -732,6 +733,10 @@ export default class DomConverter {
 	 * @returns View selection.
 	 */
 	public domSelectionToView( domSelection: DomSelection ): ViewSelection {
+		if ( isGeckoRestrictedDomSelection( domSelection ) ) {
+			return new ViewSelection( [] );
+		}
+
 		// DOM selection might be placed in fake selection container.
 		// If container contains fake selection - return corresponding view selection.
 		if ( domSelection.rangeCount === 1 ) {
@@ -1787,6 +1792,24 @@ function _logUnsafeElement( elementName: string ): void {
 	}
 }
 
+// In certain cases, Firefox mysteriously assigns so called "restricted objects" to native DOM Range properties.
+// Any attempt at accessing restricted object's properties causes errors.
+// https://github.com/ckeditor/ckeditor5/issues/9635
+function isGeckoRestrictedDomSelection( domSelection: DomSelection ): boolean {
+	if ( !env.isGecko ) {
+		return false;
+	}
+
+	try {
+		const container = domSelection.getRangeAt( 0 ).startContainer;
+		Object.prototype.toString.call( container );
+	} catch ( error ) {
+		return true;
+	}
+
+	return false;
+}
+
 /**
  * Enum representing the type of the block filler.
  *
diff --git a/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts b/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts
index 86e1b6b723a..b31a1ab2abd 100644
--- a/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts
+++ b/packages/ckeditor5-engine/src/view/observer/selectionobserver.ts
@@ -232,10 +232,6 @@ export default class SelectionObserver extends Observer {
 
 		const domSelection = domDocument.defaultView!.getSelection()!;
 
-		if ( isGeckoRestrictedDomSelection( domSelection ) ) {
-			return;
-		}
-
 		if ( this.checkShouldIgnoreEventFromTarget( domSelection.anchorNode! ) ) {
 			return;
 		}
@@ -367,21 +363,3 @@ export type ViewDocumentSelectionChangeDoneEvent = {
 	name: 'selectionChangeDone';
 	args: [ ViewDocumentSelectionEventData ];
 };
-
-// I certain cases, Firefox mysteriously assigns so called "restricted objects" to native DOM Range properties.
-// Any attempt at accessing restricted object's properties causes errors.
-// https://github.com/ckeditor/ckeditor5/issues/9635
-function isGeckoRestrictedDomSelection( domSelection: DomSelection ): boolean {
-	if ( !env.isGecko ) {
-		return false;
-	}
-
-	try {
-		const container = domSelection.getRangeAt( 0 ).startContainer;
-		Object.prototype.toString.call( container );
-	} catch ( error ) {
-		return true;
-	}
-
-	return false;
-}

From d704e48926f0b141ba8ee8b9ee25ff8bf95aabd1 Mon Sep 17 00:00:00 2001
From: Illia Sheremetov <i.sheremetov@cksource.com>
Date: Thu, 3 Aug 2023 16:14:28 +0200
Subject: [PATCH 08/16] Fix (engine): code review fixes

---
 .../ckeditor5-engine/src/view/domconverter.ts | 16 +++++++++++-----
 .../tests/view/domconverter/dom-to-view.js    | 19 +++++++++++++++++++
 2 files changed, 30 insertions(+), 5 deletions(-)

diff --git a/packages/ckeditor5-engine/src/view/domconverter.ts b/packages/ckeditor5-engine/src/view/domconverter.ts
index 2a0791a8372..6f66be40372 100644
--- a/packages/ckeditor5-engine/src/view/domconverter.ts
+++ b/packages/ckeditor5-engine/src/view/domconverter.ts
@@ -733,6 +733,7 @@ export default class DomConverter {
 	 * @returns View selection.
 	 */
 	public domSelectionToView( domSelection: DomSelection ): ViewSelection {
+		// https://github.com/ckeditor/ckeditor5/issues/9635
 		if ( isGeckoRestrictedDomSelection( domSelection ) ) {
 			return new ViewSelection( [] );
 		}
@@ -1792,17 +1793,22 @@ function _logUnsafeElement( elementName: string ): void {
 	}
 }
 
-// In certain cases, Firefox mysteriously assigns so called "restricted objects" to native DOM Range properties.
-// Any attempt at accessing restricted object's properties causes errors.
-// https://github.com/ckeditor/ckeditor5/issues/9635
+/**
+ * In certain cases, Firefox mysteriously assigns so called "restricted objects" to native DOM Range properties.
+ * Any attempt at accessing restricted object's properties causes errors.
+ * https://github.com/ckeditor/ckeditor5/issues/9635
+ */
 function isGeckoRestrictedDomSelection( domSelection: DomSelection ): boolean {
 	if ( !env.isGecko ) {
 		return false;
 	}
 
 	try {
-		const container = domSelection.getRangeAt( 0 ).startContainer;
-		Object.prototype.toString.call( container );
+		if ( domSelection.rangeCount ) {
+			const container = domSelection.getRangeAt( 0 ).startContainer;
+
+			Object.prototype.toString.call( container );
+		}
 	} catch ( error ) {
 		return true;
 	}
diff --git a/packages/ckeditor5-engine/tests/view/domconverter/dom-to-view.js b/packages/ckeditor5-engine/tests/view/domconverter/dom-to-view.js
index cb7d8a80782..04308630750 100644
--- a/packages/ckeditor5-engine/tests/view/domconverter/dom-to-view.js
+++ b/packages/ckeditor5-engine/tests/view/domconverter/dom-to-view.js
@@ -18,6 +18,7 @@ import { parse, stringify } from '../../../src/dev-utils/view';
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 import count from '@ckeditor/ckeditor5-utils/src/count';
 import createElement from '@ckeditor/ckeditor5-utils/src/dom/createelement';
+import env from '@ckeditor/ckeditor5-utils/src/env';
 
 describe( 'DomConverter', () => {
 	let converter, viewDocument;
@@ -1287,5 +1288,23 @@ describe( 'DomConverter', () => {
 
 			domContainer.remove();
 		} );
+
+		it( 'should detect "restricted objects" in Firefox DOM ranges and prevent an error being thrown', () => {
+			const domRangeStubWithRestrictedObject = document.createRange();
+
+			testUtils.sinon.stub( env, 'isGecko' ).value( true );
+
+			sinon.stub( domRangeStubWithRestrictedObject, 'startContainer' ).get( () => {
+				throw new Error( 'Permission denied to access property Symbol.toStringTag' );
+			} );
+
+			const domSelection = document.getSelection();
+
+			testUtils.sinon.stub( domSelection, 'getRangeAt' ).withArgs( 0 ).returns( domRangeStubWithRestrictedObject );
+
+			expect( () => {
+				converter.domSelectionToView( domSelection );
+			} ).to.not.throw();
+		} );
 	} );
 } );

From 24b1e1be7e63186ddcf83c352abae8ed6c5b39f0 Mon Sep 17 00:00:00 2001
From: Illia Sheremetov <i.sheremetov@cksource.com>
Date: Wed, 9 Aug 2023 11:38:23 +0200
Subject: [PATCH 09/16] Fix (engine): code review fix

---
 packages/ckeditor5-engine/src/view/domconverter.ts | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/packages/ckeditor5-engine/src/view/domconverter.ts b/packages/ckeditor5-engine/src/view/domconverter.ts
index 6f66be40372..deebd3c70a6 100644
--- a/packages/ckeditor5-engine/src/view/domconverter.ts
+++ b/packages/ckeditor5-engine/src/view/domconverter.ts
@@ -1799,16 +1799,14 @@ function _logUnsafeElement( elementName: string ): void {
  * https://github.com/ckeditor/ckeditor5/issues/9635
  */
 function isGeckoRestrictedDomSelection( domSelection: DomSelection ): boolean {
-	if ( !env.isGecko ) {
+	if ( !env.isGecko || !domSelection.rangeCount ) {
 		return false;
 	}
 
 	try {
-		if ( domSelection.rangeCount ) {
-			const container = domSelection.getRangeAt( 0 ).startContainer;
+		const container = domSelection.getRangeAt( 0 ).startContainer;
 
-			Object.prototype.toString.call( container );
-		}
+		Object.prototype.toString.call( container );
 	} catch ( error ) {
 		return true;
 	}

From 1dfc78349c07e306048912b50a9ad2db659b9df7 Mon Sep 17 00:00:00 2001
From: Kuba Niegowski <j.niegowski@cksource.com>
Date: Mon, 21 Aug 2023 17:10:04 +0200
Subject: [PATCH 10/16] Updated tests.

---
 .../ckeditor5-engine/src/view/domconverter.ts | 10 ++-
 .../tests/view/domconverter/dom-to-view.js    | 87 ++++++++++++++++---
 2 files changed, 84 insertions(+), 13 deletions(-)

diff --git a/packages/ckeditor5-engine/src/view/domconverter.ts b/packages/ckeditor5-engine/src/view/domconverter.ts
index deebd3c70a6..7b9aa9f1a01 100644
--- a/packages/ckeditor5-engine/src/view/domconverter.ts
+++ b/packages/ckeditor5-engine/src/view/domconverter.ts
@@ -1799,13 +1799,17 @@ function _logUnsafeElement( elementName: string ): void {
  * https://github.com/ckeditor/ckeditor5/issues/9635
  */
 function isGeckoRestrictedDomSelection( domSelection: DomSelection ): boolean {
-	if ( !env.isGecko || !domSelection.rangeCount ) {
+	if ( !env.isGecko ) {
 		return false;
 	}
 
-	try {
-		const container = domSelection.getRangeAt( 0 ).startContainer;
+	if ( !domSelection.rangeCount ) {
+		return false;
+	}
 
+	const container = domSelection.getRangeAt( 0 ).startContainer;
+
+	try {
 		Object.prototype.toString.call( container );
 	} catch ( error ) {
 		return true;
diff --git a/packages/ckeditor5-engine/tests/view/domconverter/dom-to-view.js b/packages/ckeditor5-engine/tests/view/domconverter/dom-to-view.js
index 04308630750..9fed9fa73e2 100644
--- a/packages/ckeditor5-engine/tests/view/domconverter/dom-to-view.js
+++ b/packages/ckeditor5-engine/tests/view/domconverter/dom-to-view.js
@@ -9,6 +9,7 @@ import ViewElement from '../../../src/view/element';
 import ViewUIElement from '../../../src/view/uielement';
 import ViewDocument from '../../../src/view/document';
 import ViewDocumentSelection from '../../../src/view/documentselection';
+import ViewSelection from '../../../src/view/selection';
 import DomConverter from '../../../src/view/domconverter';
 import ViewDocumentFragment from '../../../src/view/documentfragment';
 import { BR_FILLER, INLINE_FILLER, INLINE_FILLER_LENGTH, NBSP_FILLER } from '../../../src/view/filler';
@@ -1289,22 +1290,88 @@ describe( 'DomConverter', () => {
 			domContainer.remove();
 		} );
 
-		it( 'should detect "restricted objects" in Firefox DOM ranges and prevent an error being thrown', () => {
-			const domRangeStubWithRestrictedObject = document.createRange();
+		// See https://github.com/ckeditor/ckeditor5/issues/9635.
+		describe( 'restricted objects in Firefox', () => {
+			it( 'not throw if selection is anchored in the restricted object', () => {
+				testUtils.sinon.stub( env, 'isGecko' ).value( true );
 
-			testUtils.sinon.stub( env, 'isGecko' ).value( true );
+				const domFoo = document.createTextNode( 'foo' );
+				const domP = createElement( document, 'p', null, [ domFoo ] );
 
-			sinon.stub( domRangeStubWithRestrictedObject, 'startContainer' ).get( () => {
-				throw new Error( 'Permission denied to access property Symbol.toStringTag' );
+				const viewP = parse( '<p>foo</p>' );
+
+				converter.bindElements( domP, viewP );
+
+				document.body.appendChild( domP );
+
+				const domRange = document.createRange();
+				domRange.setStart( domFoo, 1 );
+				domRange.setEnd( domFoo, 2 );
+
+				const domSelection = document.getSelection();
+				domSelection.removeAllRanges();
+				domSelection.addRange( domRange );
+
+				const viewSelection = converter.domSelectionToView( domSelection );
+
+				expect( viewSelection.rangeCount ).to.equal( 1 );
+				expect( stringify( viewP, viewSelection.getFirstRange() ) ).to.equal( '<p>f{o}o</p>' );
+
+				// Now we know that there should be a valid view range. So let's test if the DOM node throws an error.
+				sinon.stub( domFoo, Symbol.toStringTag ).get( () => {
+					throw new Error( 'Permission denied to access property Symbol.toStringTag' );
+				} );
+
+				let result = null;
+
+				expect( () => {
+					result = converter.domSelectionToView( domSelection );
+				} ).to.not.throw();
+
+				expect( result instanceof ViewSelection ).to.be.true;
+				expect( result.rangeCount ).to.equal( 0 );
+
+				domP.remove();
 			} );
 
-			const domSelection = document.getSelection();
+			it( 'should not check if restricted object on non-Gecko browsers', () => {
+				testUtils.sinon.stub( env, 'isGecko' ).value( false );
 
-			testUtils.sinon.stub( domSelection, 'getRangeAt' ).withArgs( 0 ).returns( domRangeStubWithRestrictedObject );
+				const domFoo = document.createTextNode( 'foo' );
+				const domP = createElement( document, 'p', null, [ domFoo ] );
 
-			expect( () => {
-				converter.domSelectionToView( domSelection );
-			} ).to.not.throw();
+				const viewP = parse( '<p>foo</p>' );
+
+				converter.bindElements( domP, viewP );
+
+				document.body.appendChild( domP );
+
+				const domRange = document.createRange();
+				domRange.setStart( domFoo, 1 );
+				domRange.setEnd( domFoo, 2 );
+
+				const domSelection = document.getSelection();
+				domSelection.removeAllRanges();
+				domSelection.addRange( domRange );
+
+				const viewSelection = converter.domSelectionToView( domSelection );
+
+				expect( viewSelection.rangeCount ).to.equal( 1 );
+				expect( stringify( viewP, viewSelection.getFirstRange() ) ).to.equal( '<p>f{o}o</p>' );
+
+				domP.remove();
+			} );
+
+			it( 'should convert empty selection to empty selection (in Gecko)', () => {
+				testUtils.sinon.stub( env, 'isGecko' ).value( true );
+
+				const domSelection = document.getSelection();
+				domSelection.removeAllRanges();
+
+				const viewSelection = converter.domSelectionToView( domSelection );
+
+				expect( viewSelection.rangeCount ).to.equal( 0 );
+			} );
 		} );
 	} );
 } );

From 10fc9f2b4c861416877fdef06910d8a509ff41e6 Mon Sep 17 00:00:00 2001
From: Illia Sheremetov <i.sheremetov@cksource.com>
Date: Tue, 22 Aug 2023 12:01:57 +0200
Subject: [PATCH 11/16] Fix (engine): code review fixes

---
 .../ckeditor5-engine/src/view/domconverter.ts |  4 +--
 .../tests/view/observer/selectionobserver.js  | 30 +------------------
 2 files changed, 3 insertions(+), 31 deletions(-)

diff --git a/packages/ckeditor5-engine/src/view/domconverter.ts b/packages/ckeditor5-engine/src/view/domconverter.ts
index 7b9aa9f1a01..46410da8ec4 100644
--- a/packages/ckeditor5-engine/src/view/domconverter.ts
+++ b/packages/ckeditor5-engine/src/view/domconverter.ts
@@ -733,7 +733,7 @@ export default class DomConverter {
 	 * @returns View selection.
 	 */
 	public domSelectionToView( domSelection: DomSelection ): ViewSelection {
-		// https://github.com/ckeditor/ckeditor5/issues/9635
+		// See: https://github.com/ckeditor/ckeditor5/issues/9635.
 		if ( isGeckoRestrictedDomSelection( domSelection ) ) {
 			return new ViewSelection( [] );
 		}
@@ -1796,7 +1796,7 @@ function _logUnsafeElement( elementName: string ): void {
 /**
  * In certain cases, Firefox mysteriously assigns so called "restricted objects" to native DOM Range properties.
  * Any attempt at accessing restricted object's properties causes errors.
- * https://github.com/ckeditor/ckeditor5/issues/9635
+ * See: https://github.com/ckeditor/ckeditor5/issues/9635.
  */
 function isGeckoRestrictedDomSelection( domSelection: DomSelection ): boolean {
 	if ( !env.isGecko ) {
diff --git a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
index 0e3e22efba8..32032666d5f 100644
--- a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
+++ b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
@@ -3,7 +3,7 @@
  * For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
  */
 
-/* globals setTimeout, document, console, Event, Selection */
+/* globals setTimeout, document, console, Event */
 
 import testUtils from '@ckeditor/ckeditor5-core/tests/_utils/utils';
 
@@ -162,34 +162,6 @@ describe( 'SelectionObserver', () => {
 		changeDomSelection();
 	} );
 
-	describe( 'Restricted objects handling in Gecko', () => {
-		beforeEach( () => {
-			testUtils.sinon.stub( env, 'isGecko' ).value( true );
-		} );
-
-		it( 'should detect "restricted objects" in Firefox DOM ranges and prevent an error being thrown', done => {
-			const domRangeStubWithRestrictedObject = domDocument.createRange();
-
-			sinon.stub( domRangeStubWithRestrictedObject, 'startContainer' ).get( () => {
-				throw new Error( 'Permission denied to access property Symbol.toStringTag' );
-			} );
-
-			testUtils.sinon.stub( Selection.prototype, 'getRangeAt' ).returns( domRangeStubWithRestrictedObject );
-
-			expect( () => {
-				changeDomSelection();
-				setTimeout( done, 100 );
-			} ).to.not.throw();
-		} );
-
-		it( 'should do nothing in Firefox if the DOM selection is correct', done => {
-			expect( () => {
-				changeDomSelection();
-				setTimeout( done, 100 );
-			} ).to.not.throw();
-		} );
-	} );
-
 	it( 'should add only one #selectionChange listener to one document', done => {
 		// Add second roots to ensure that listener is added once.
 		createViewRoot( viewDocument, 'div', 'additional' );

From 1ff25a4b5cb83213a6c1c4a059246fe58c3672af Mon Sep 17 00:00:00 2001
From: Illia Sheremetov <i.sheremetov@cksource.com>
Date: Tue, 22 Aug 2023 13:09:00 +0200
Subject: [PATCH 12/16] Fix (engine): fix test

---
 .../tests/view/observer/selectionobserver.js  | 80 ++++++++++++++++++-
 1 file changed, 78 insertions(+), 2 deletions(-)

diff --git a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
index 32032666d5f..0160d69f9ce 100644
--- a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
+++ b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
@@ -15,12 +15,14 @@ import SelectionObserver from '../../../src/view/observer/selectionobserver';
 import FocusObserver from '../../../src/view/observer/focusobserver';
 import MutationObserver from '../../../src/view/observer/mutationobserver';
 import createViewRoot from '../_utils/createroot';
-import { parse } from '../../../src/dev-utils/view';
+import DomConverter from '../../../src/view/domconverter';
+import { parse, stringify } from '../../../src/dev-utils/view';
 import { StylesProcessor } from '../../../src/view/stylesmap';
+import createElement from '@ckeditor/ckeditor5-utils/src/dom/createelement';
 import env from '@ckeditor/ckeditor5-utils/src/env';
 
 describe( 'SelectionObserver', () => {
-	let view, viewDocument, viewRoot, selectionObserver, domRoot, domMain, domDocument;
+	let view, viewDocument, viewRoot, selectionObserver, domRoot, domMain, domDocument, converter;
 
 	testUtils.createSinonSandbox();
 
@@ -30,6 +32,7 @@ describe( 'SelectionObserver', () => {
 		domRoot.innerHTML = '<div contenteditable="true"></div><div contenteditable="true" id="additional"></div>';
 		domMain = domRoot.childNodes[ 0 ];
 		domDocument.body.appendChild( domRoot );
+		converter = new DomConverter( viewDocument );
 
 		view = new View( new StylesProcessor() );
 		viewDocument = view.document;
@@ -162,6 +165,79 @@ describe( 'SelectionObserver', () => {
 		changeDomSelection();
 	} );
 
+	describe( 'Restricted objects handling in Gecko', () => {
+		beforeEach( () => {
+			testUtils.sinon.stub( env, 'isGecko' ).value( true );
+		} );
+
+		it( 'should detect "restricted objects" in Firefox DOM ranges and prevent an error being thrown', () => {
+			testUtils.sinon.stub( env, 'isGecko' ).value( true );
+
+			const domFoo = document.createTextNode( 'foo' );
+			const domP = createElement( document, 'p', null, [ domFoo ] );
+
+			const viewP = parse( '<p>foo</p>' );
+
+			converter.bindElements( domP, viewP );
+
+			document.body.appendChild( domP );
+
+			const domRange = document.createRange();
+			domRange.setStart( domFoo, 1 );
+			domRange.setEnd( domFoo, 2 );
+
+			const domSelection = document.getSelection();
+			domSelection.removeAllRanges();
+			domSelection.addRange( domRange );
+
+			const viewSelection = converter.domSelectionToView( domSelection );
+
+			expect( viewSelection.rangeCount ).to.equal( 1 );
+			expect( stringify( viewP, viewSelection.getFirstRange() ) ).to.equal( '<p>f{o}o</p>' );
+
+			// Now we know that there should be a valid view range. So let's test if the DOM node throws an error.
+			sinon.stub( domFoo, Symbol.toStringTag ).get( () => {
+				throw new Error( 'Permission denied to access property Symbol.toStringTag' );
+			} );
+
+			let result = null;
+
+			expect( () => {
+				result = converter.domSelectionToView( domSelection );
+			} ).to.not.throw();
+
+			expect( result instanceof ViewSelection ).to.be.true;
+			expect( result.rangeCount ).to.equal( 0 );
+
+			domP.remove();
+		} );
+
+		it( 'should do nothing in Firefox if the DOM selection is correct', done => {
+			expect( () => {
+				const domFoo = document.createTextNode( 'foo' );
+				const domP = createElement( document, 'p', null, [ domFoo ] );
+
+				const viewP = parse( '<p>foo</p>' );
+
+				converter.bindElements( domP, viewP );
+
+				document.body.appendChild( domP );
+
+				const domRange = document.createRange();
+				domRange.setStart( domFoo, 1 );
+				domRange.setEnd( domFoo, 2 );
+
+				const domSelection = document.getSelection();
+				domSelection.removeAllRanges();
+				domSelection.addRange( domRange );
+
+				converter.domSelectionToView( domSelection );
+
+				setTimeout( done, 100 );
+			} ).to.not.throw();
+		} );
+	} );
+
 	it( 'should add only one #selectionChange listener to one document', done => {
 		// Add second roots to ensure that listener is added once.
 		createViewRoot( viewDocument, 'div', 'additional' );

From 34ace0193eb47767c0fab8fbaf7bb6910101be95 Mon Sep 17 00:00:00 2001
From: Illia Sheremetov <i.sheremetov@cksource.com>
Date: Tue, 22 Aug 2023 13:48:56 +0200
Subject: [PATCH 13/16] Fix (engine): fix test

---
 .../tests/view/observer/selectionobserver.js  | 26 ++++++++++---------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
index 0160d69f9ce..dcdd301c200 100644
--- a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
+++ b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
@@ -213,28 +213,30 @@ describe( 'SelectionObserver', () => {
 		} );
 
 		it( 'should do nothing in Firefox if the DOM selection is correct', done => {
-			expect( () => {
-				const domFoo = document.createTextNode( 'foo' );
-				const domP = createElement( document, 'p', null, [ domFoo ] );
+			const domFoo = document.createTextNode( 'foo' );
+			const domP = createElement( document, 'p', null, [ domFoo ] );
 
-				const viewP = parse( '<p>foo</p>' );
+			const viewP = parse( '<p>foo</p>' );
 
-				converter.bindElements( domP, viewP );
+			converter.bindElements( domP, viewP );
 
-				document.body.appendChild( domP );
+			document.body.appendChild( domP );
 
-				const domRange = document.createRange();
-				domRange.setStart( domFoo, 1 );
-				domRange.setEnd( domFoo, 2 );
+			const domRange = document.createRange();
+			domRange.setStart( domFoo, 1 );
+			domRange.setEnd( domFoo, 2 );
 
-				const domSelection = document.getSelection();
-				domSelection.removeAllRanges();
-				domSelection.addRange( domRange );
+			const domSelection = document.getSelection();
+			domSelection.removeAllRanges();
+			domSelection.addRange( domRange );
 
+			expect( () => {
 				converter.domSelectionToView( domSelection );
 
 				setTimeout( done, 100 );
 			} ).to.not.throw();
+
+			domP.remove();
 		} );
 	} );
 

From 7b953f139e08711943dc21961e56b96c5860a853 Mon Sep 17 00:00:00 2001
From: Illia Sheremetov <i.sheremetov@cksource.com>
Date: Tue, 29 Aug 2023 11:33:33 +0200
Subject: [PATCH 14/16] Test (engine): code review fix

---
 .../tests/view/observer/selectionobserver.js               | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
index dcdd301c200..eca4c09cd60 100644
--- a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
+++ b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
@@ -15,14 +15,13 @@ import SelectionObserver from '../../../src/view/observer/selectionobserver';
 import FocusObserver from '../../../src/view/observer/focusobserver';
 import MutationObserver from '../../../src/view/observer/mutationobserver';
 import createViewRoot from '../_utils/createroot';
-import DomConverter from '../../../src/view/domconverter';
 import { parse, stringify } from '../../../src/dev-utils/view';
 import { StylesProcessor } from '../../../src/view/stylesmap';
 import createElement from '@ckeditor/ckeditor5-utils/src/dom/createelement';
 import env from '@ckeditor/ckeditor5-utils/src/env';
 
 describe( 'SelectionObserver', () => {
-	let view, viewDocument, viewRoot, selectionObserver, domRoot, domMain, domDocument, converter;
+	let view, viewDocument, viewRoot, selectionObserver, domRoot, domMain, domDocument;
 
 	testUtils.createSinonSandbox();
 
@@ -32,8 +31,6 @@ describe( 'SelectionObserver', () => {
 		domRoot.innerHTML = '<div contenteditable="true"></div><div contenteditable="true" id="additional"></div>';
 		domMain = domRoot.childNodes[ 0 ];
 		domDocument.body.appendChild( domRoot );
-		converter = new DomConverter( viewDocument );
-
 		view = new View( new StylesProcessor() );
 		viewDocument = view.document;
 		createViewRoot( viewDocument );
@@ -175,6 +172,7 @@ describe( 'SelectionObserver', () => {
 
 			const domFoo = document.createTextNode( 'foo' );
 			const domP = createElement( document, 'p', null, [ domFoo ] );
+			const converter = view.domConverter;
 
 			const viewP = parse( '<p>foo</p>' );
 
@@ -215,6 +213,7 @@ describe( 'SelectionObserver', () => {
 		it( 'should do nothing in Firefox if the DOM selection is correct', done => {
 			const domFoo = document.createTextNode( 'foo' );
 			const domP = createElement( document, 'p', null, [ domFoo ] );
+			const converter = view.domConverter;
 
 			const viewP = parse( '<p>foo</p>' );
 

From 95afdeb4260dcae4a9562fde5d01899c0324497d Mon Sep 17 00:00:00 2001
From: Illia Sheremetov <i.sheremetov@cksource.com>
Date: Wed, 30 Aug 2023 09:58:35 +0200
Subject: [PATCH 15/16] Test (engine): test fix

---
 .../tests/view/observer/selectionobserver.js  | 82 +++----------------
 1 file changed, 11 insertions(+), 71 deletions(-)

diff --git a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
index eca4c09cd60..7ebe11a9de7 100644
--- a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
+++ b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
@@ -15,9 +15,8 @@ import SelectionObserver from '../../../src/view/observer/selectionobserver';
 import FocusObserver from '../../../src/view/observer/focusobserver';
 import MutationObserver from '../../../src/view/observer/mutationobserver';
 import createViewRoot from '../_utils/createroot';
-import { parse, stringify } from '../../../src/dev-utils/view';
+import { parse } from '../../../src/dev-utils/view';
 import { StylesProcessor } from '../../../src/view/stylesmap';
-import createElement from '@ckeditor/ckeditor5-utils/src/dom/createelement';
 import env from '@ckeditor/ckeditor5-utils/src/env';
 
 describe( 'SelectionObserver', () => {
@@ -162,81 +161,23 @@ describe( 'SelectionObserver', () => {
 		changeDomSelection();
 	} );
 
-	describe( 'Restricted objects handling in Gecko', () => {
-		beforeEach( () => {
-			testUtils.sinon.stub( env, 'isGecko' ).value( true );
-		} );
-
-		it( 'should detect "restricted objects" in Firefox DOM ranges and prevent an error being thrown', () => {
-			testUtils.sinon.stub( env, 'isGecko' ).value( true );
-
-			const domFoo = document.createTextNode( 'foo' );
-			const domP = createElement( document, 'p', null, [ domFoo ] );
-			const converter = view.domConverter;
-
-			const viewP = parse( '<p>foo</p>' );
-
-			converter.bindElements( domP, viewP );
-
-			document.body.appendChild( domP );
-
-			const domRange = document.createRange();
-			domRange.setStart( domFoo, 1 );
-			domRange.setEnd( domFoo, 2 );
-
-			const domSelection = document.getSelection();
-			domSelection.removeAllRanges();
-			domSelection.addRange( domRange );
-
-			const viewSelection = converter.domSelectionToView( domSelection );
-
-			expect( viewSelection.rangeCount ).to.equal( 1 );
-			expect( stringify( viewP, viewSelection.getFirstRange() ) ).to.equal( '<p>f{o}o</p>' );
-
-			// Now we know that there should be a valid view range. So let's test if the DOM node throws an error.
-			sinon.stub( domFoo, Symbol.toStringTag ).get( () => {
-				throw new Error( 'Permission denied to access property Symbol.toStringTag' );
-			} );
+	it( 'should detect "restricted objects" in Firefox DOM ranges and prevent an error being thrown', () => {
+		testUtils.sinon.stub( env, 'isGecko' ).value( true );
 
-			let result = null;
+		changeDomSelection();
+		domDocument.dispatchEvent( new Event( 'selectionchange' ) );
 
-			expect( () => {
-				result = converter.domSelectionToView( domSelection );
-			} ).to.not.throw();
+		expect( view.hasDomSelection ).to.be.true;
 
-			expect( result instanceof ViewSelection ).to.be.true;
-			expect( result.rangeCount ).to.equal( 0 );
+		const domFoo = domDocument.getSelection().anchorNode;
 
-			domP.remove();
+		sinon.stub( domFoo, Symbol.toStringTag ).get( () => {
+			throw new Error( 'Permission denied to access property Symbol.toStringTag' );
 		} );
 
-		it( 'should do nothing in Firefox if the DOM selection is correct', done => {
-			const domFoo = document.createTextNode( 'foo' );
-			const domP = createElement( document, 'p', null, [ domFoo ] );
-			const converter = view.domConverter;
-
-			const viewP = parse( '<p>foo</p>' );
-
-			converter.bindElements( domP, viewP );
-
-			document.body.appendChild( domP );
-
-			const domRange = document.createRange();
-			domRange.setStart( domFoo, 1 );
-			domRange.setEnd( domFoo, 2 );
-
-			const domSelection = document.getSelection();
-			domSelection.removeAllRanges();
-			domSelection.addRange( domRange );
-
-			expect( () => {
-				converter.domSelectionToView( domSelection );
-
-				setTimeout( done, 100 );
-			} ).to.not.throw();
+		domDocument.dispatchEvent( new Event( 'selectionchange' ) );
 
-			domP.remove();
-		} );
+		expect( view.hasDomSelection ).to.be.false;
 	} );
 
 	it( 'should add only one #selectionChange listener to one document', done => {
@@ -547,7 +488,6 @@ describe( 'SelectionObserver', () => {
 			selectionObserver.listenTo( domMain, 'selectstart', selectStartChangedSpy, { priority: 'highest' } );
 
 			// The event was fired somewhere else in DOM.
-			domDocument.dispatchEvent( new Event( 'selectstart' ) );
 
 			expect( viewDocument.isSelecting ).to.be.false;
 			sinon.assert.notCalled( selectStartChangedSpy );

From a95c15702e40f18cf45aad30a5bfd9a7f07fe531 Mon Sep 17 00:00:00 2001
From: Illia Sheremetov <i.sheremetov@cksource.com>
Date: Wed, 30 Aug 2023 12:58:07 +0200
Subject: [PATCH 16/16] Test (engine): fix test

---
 .../ckeditor5-engine/tests/view/observer/selectionobserver.js    | 1 +
 1 file changed, 1 insertion(+)

diff --git a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
index 7ebe11a9de7..7da556de42b 100644
--- a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
+++ b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
@@ -488,6 +488,7 @@ describe( 'SelectionObserver', () => {
 			selectionObserver.listenTo( domMain, 'selectstart', selectStartChangedSpy, { priority: 'highest' } );
 
 			// The event was fired somewhere else in DOM.
+			domDocument.dispatchEvent( new Event( 'selectstart' ) );
 
 			expect( viewDocument.isSelecting ).to.be.false;
 			sinon.assert.notCalled( selectStartChangedSpy );