--- a/browser/base/content/tabview/tabitems.js
+++ b/browser/base/content/tabview/tabitems.js
@@ -19,16 +19,17 @@
  * the Initial Developer. All Rights Reserved.
  *
  * Contributor(s):
  * Ian Gilman <ian@iangilman.com>
  * Aza Raskin <aza@mozilla.com>
  * Michael Yoshitaka Erlewine <mitcho@mitcho.com>
  * Ehsan Akhgari <ehsan@mozilla.com>
  * Raymond Lee <raymond@appcoast.com>
+ * Tim Taubert <tim.taubert@gmx.de>
  *
  * Alternatively, the contents of this file may be used under the terms of
  * either the GNU General Public License Version 2 or later (the "GPL"), or
  * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
  * in which case the provisions of the GPL or the LGPL are applicable instead
  * of those above. If you wish to allow use of your version of this file only
  * under the terms of either the GPL or the LGPL, and not to allow others to
  * use your version of this file under the terms of the MPL, indicate your
@@ -57,17 +58,17 @@ function TabItem(tab, options) {
 
   if (!options)
     options = {};
 
   // ___ set up div
   var $div = iQ('<div>')
     .addClass('tab')
     .html("<div class='thumb'>" +
-          "<img class='cached-thumb' style='display:none'/><canvas moz-opaque='true'/></div>" +
+          "<img class='cached-thumb' style='display:none'/><canvas moz-opaque/></div>" +
           "<div class='favicon'><img/></div>" +
           "<span class='tab-title'>&nbsp;</span>"
     )
     .appendTo('body');
 
   this._cachedImageData = null;
   this.shouldHideCachedData = false;
   this.canvasSizeForced = false;
@@ -803,17 +804,17 @@ let TabItems = {
   // Set up the necessary tracking to maintain the <TabItems>s.
   init: function TabItems_init() {
     Utils.assert(window.AllTabs, "AllTabs must be initialized first");
     let self = this;
     
     this.minTabHeight = this.minTabWidth * this.tabHeight / this.tabWidth;
 
     let $canvas = iQ("<canvas>")
-      .attr('moz-opaque', true);
+      .attr('moz-opaque', '');
     $canvas.appendTo(iQ("body"));
     $canvas.hide();
     this.tempCanvas = $canvas[0];
     // 150 pixels is an empirical size, below which FF's drawWindow()
     // algorithm breaks down
     this.tempCanvas.width = 150;
     this.tempCanvas.height = 150;