--- a/mobile/chrome/content/LoginManagerChild.js
+++ b/mobile/chrome/content/LoginManagerChild.js
@@ -831,17 +831,17 @@ var loginManager = {
                     }
                     return;
 
                 case "DOMContentLoaded":
                     this._pwmgr._fillDocument(event.target);
                     break;
 
                 case "unload":
-                    Services.prefs.removeObserver("signon.", this._pwmgr);
+                    Services.prefs.removeObserver("signon.", this._pwmgr._observer);
                     Services.obs.removeObserver(this._pwmgr._observer, "earlyformsubmit");
                     break;
 
                 default:
                     this._pwmgr.log("Oops! This event unexpected.");
                     return;
             }
         }