diff --git a/toolkit/components/url-classifier/content/moz/preferences.js b/toolkit/components/url-classifier/content/moz/preferences.js
index 8dfb95f4f0f7..bf85ca3e0344 100644
--- a/toolkit/components/url-classifier/content/moz/preferences.js
+++ b/toolkit/components/url-classifier/content/moz/preferences.js
@@ -254,7 +254,6 @@ G_PreferenceObserver.prototype.observe = function(subject, topic, data) {
  * @param iid Interface id of the interface the caller wants
  */
 G_PreferenceObserver.prototype.QueryInterface = function(iid) {
-  var Ci = Ci;
   if (iid.equals(Ci.nsISupports) || 
       iid.equals(Ci.nsIObserver) ||
       iid.equals(Ci.nsISupportsWeakReference))