diff --git a/packages/ckeditor5-engine/src/view/domconverter.ts b/packages/ckeditor5-engine/src/view/domconverter.ts
index d7c0ae8357a..46410da8ec4 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 +733,11 @@ export default class DomConverter {
 	 * @returns View selection.
 	 */
 	public domSelectionToView( domSelection: DomSelection ): ViewSelection {
+		// See: https://github.com/ckeditor/ckeditor5/issues/9635.
+		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 +1793,31 @@ 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.
+ * See: https://github.com/ckeditor/ckeditor5/issues/9635.
+ */
+function isGeckoRestrictedDomSelection( domSelection: DomSelection ): boolean {
+	if ( !env.isGecko ) {
+		return false;
+	}
+
+	if ( !domSelection.rangeCount ) {
+		return false;
+	}
+
+	const container = domSelection.getRangeAt( 0 ).startContainer;
+
+	try {
+		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/tests/view/domconverter/dom-to-view.js b/packages/ckeditor5-engine/tests/view/domconverter/dom-to-view.js
index cb7d8a80782..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';
@@ -18,6 +19,7 @@ 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 +1289,89 @@ describe( 'DomConverter', () => {
 
 			domContainer.remove();
 		} );
+
+		// 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 );
+
+				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 not check if restricted object on non-Gecko browsers', () => {
+				testUtils.sinon.stub( env, 'isGecko' ).value( false );
+
+				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>' );
+
+				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 );
+			} );
+		} );
 	} );
 } );
diff --git a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
index 32032666d5f..7da556de42b 100644
--- a/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
+++ b/packages/ckeditor5-engine/tests/view/observer/selectionobserver.js
@@ -30,7 +30,6 @@ describe( 'SelectionObserver', () => {
 		domRoot.innerHTML = '<div contenteditable="true"></div><div contenteditable="true" id="additional"></div>';
 		domMain = domRoot.childNodes[ 0 ];
 		domDocument.body.appendChild( domRoot );
-
 		view = new View( new StylesProcessor() );
 		viewDocument = view.document;
 		createViewRoot( viewDocument );
@@ -162,6 +161,25 @@ describe( 'SelectionObserver', () => {
 		changeDomSelection();
 	} );
 
+	it( 'should detect "restricted objects" in Firefox DOM ranges and prevent an error being thrown', () => {
+		testUtils.sinon.stub( env, 'isGecko' ).value( true );
+
+		changeDomSelection();
+		domDocument.dispatchEvent( new Event( 'selectionchange' ) );
+
+		expect( view.hasDomSelection ).to.be.true;
+
+		const domFoo = domDocument.getSelection().anchorNode;
+
+		sinon.stub( domFoo, Symbol.toStringTag ).get( () => {
+			throw new Error( 'Permission denied to access property Symbol.toStringTag' );
+		} );
+
+		domDocument.dispatchEvent( new Event( 'selectionchange' ) );
+
+		expect( view.hasDomSelection ).to.be.false;
+	} );
+
 	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' );