Fix (engine): detecting restricted objects in firefox

packages/ckeditor5-engine/src/view/observer/selectionobserver.ts

@@ -232,6 +232,10 @@ export default class SelectionObserver extends Observer {
 
 		const domSelection = domDocument.defaultView!.getSelection()!;
 
+		if ( isGeckoRestrictedDomSelection( domSelection ) ) {
+			return;
+		}
+
 		if ( this.checkShouldIgnoreEventFromTarget( domSelection.anchorNode! ) ) {
 			return;
 		}
@@ -363,3 +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;
+}

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';
 
@@ -162,6 +162,34 @@ 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' );