disable goldens on Firefox

Author: yjbanov

lib/web_ui/test/canvaskit/canvas_golden_test.dart

@@ -58,7 +58,8 @@ void testMain() {
       expect(restoredPixels.buffer.asUint8List(), originalPixels.buffer.asUint8List());
     });
   // TODO: https://github.com/flutter/flutter/issues/60040
-  }, skip: isIosSafari);
+  // TODO: https://github.com/flutter/flutter/issues/71520
+  }, skip: isIosSafari || isFirefox);
 }
 
 void drawTestPicture(CkCanvas canvas) {

lib/web_ui/test/canvaskit/common.dart

@@ -7,11 +7,14 @@ import 'package:test/test.dart';
 import 'package:ui/src/engine.dart';
 import 'package:ui/ui.dart' as ui;
 
-/// Whether we are running on iOS Safari.
+/// Whether the current browser is Safari on iOS.
 // TODO: https://github.com/flutter/flutter/issues/60040
 bool get isIosSafari => browserEngine == BrowserEngine.webkit &&
           operatingSystem == OperatingSystem.iOs;
 
+/// Whether the current browser is Firefox.
+bool get isFirefox => browserEngine == BrowserEngine.firefox;
+
 /// Used in tests instead of [ProductionCollector] to control Skia object
 /// collection explicitly, and to prevent leaks across tests.
 ///