Updated flex CSS prefix for Firefox.

tools/dom/templates/html/impl/impl_CSSStyleDeclaration.darttemplate

 // Copyright (c) 2012, 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.
 
 part of $LIBRARYNAME;
 
 $(ANNOTATIONS)$(CLASS_MODIFIERS) class $CLASSNAME $EXTENDS with 
     $(CLASSNAME)Base $IMPLEMENTS$NATIVESPEC {
   factory $CLASSNAME() => new CssStyleDeclaration.css('');
 
@@ skipping 1204 matching lines @@
   /** Gets the value of "filter" */
   String get filter =>
     getPropertyValue('${Device.cssPrefix}filter');
 
   /** Sets the value of "filter" */
   void set filter(String value) {
     setProperty('${Device.cssPrefix}filter', value, '');
   }
 
   /** Gets the value of "flex" */
-  String get flex =>
-    getPropertyValue('${Device.cssPrefix}flex');
+  String get flex {
+    String prefix = Device.cssPrefix
+    if (Device.isFirefox) prefix = '';
+    return getPropertyValue('${prefix}flex');
+  }
 
   /** Sets the value of "flex" */
   void set flex(String value) {
-    setProperty('${Device.cssPrefix}flex', value, '');
+    String prefix = Device.cssPrefix
+    if (Device.isFirefox) prefix = '';
+    setProperty('${prefix}flex', value, '');
   }
 
   /** Gets the value of "flex-basis" */
   String get flexBasis =>
     getPropertyValue('${Device.cssPrefix}flex-basis');
 
   /** Sets the value of "flex-basis" */
   void set flexBasis(String value) {
     setProperty('${Device.cssPrefix}flex-basis', value, '');
   }
@@ skipping 2006 matching lines @@
 
   /** Gets the value of "zoom" */
   String get zoom =>
     getPropertyValue('zoom');
 
   /** Sets the value of "zoom" */
   void set zoom(String value) {
     setProperty('zoom', value, '');
   }
 }