Make Try Dart tests run on Firefox.

dart/site/try/src/editor.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library trydart.editor;
 
 import 'dart:html';
 
 import 'package:compiler/implementation/scanner/scannerlib.dart' show
     EOF_TOKEN,
     ErrorToken,
     StringScanner,
     Token;
 
 import 'ui.dart' show
     currentTheme,
     hackDiv,
     mainEditorPane,
     observer,
     outputDiv;
 
 import 'decoration.dart' show
     CodeCompletionDecoration,
     Decoration,
     DiagnosticDecoration,
     error,
     info,
     warning;
 
+import 'selection.dart' show
+    isCollapsed;
+
 const String INDENT = '\u{a0}\u{a0}';
 
 Set<String> seenIdentifiers;
 
 Element moveActive(int distance) {
   List<Element> entries = document.querySelectorAll('.dart-static>.dart-entry');
   int activeIndex = -1;
   for (var i = 0; i < entries.length; i++) {
     if (entries[i].classes.contains('activeEntry')) {
       activeIndex = i;
@@ skipping 59 matching lines @@
   return hidden;
 }
 
 var activeCompletion;
 num minSuggestionWidth = 0;
 
 /// Returns the [Element] which encloses the current collapsed selection, if it
 /// exists.
 Element getElementAtSelection() {
   Selection selection = window.getSelection();
-  if (!selection.isCollapsed) return null;
+  if (!isCollapsed(selection)) return null;
   var anchorNode = selection.anchorNode;
   if (!mainEditorPane.contains(anchorNode)) return null;
   if (mainEditorPane == anchorNode) return null;
   int type = anchorNode.nodeType;
   if (type != Node.TEXT_NODE) return null;
   Text text = anchorNode;
   var parent = text.parent;
   if (parent is! Element) return null;
   if (mainEditorPane == parent) return null;
   return parent;
@@ skipping 102 matching lines @@
 
 diagnostic(text, tip) {
   if (text is String) {
     text = new Text(text);
   }
   return new AnchorElement()
       ..classes.add('diagnostic')
       ..append(text)
       ..append(tip);
 }