Fix (engine): detecting restricted objects in firefox

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;
 	}

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();
+		} );
 	} );
 } );