diff --git a/testing/mochitest/tests/SimpleTest/specialpowersAPI.js b/testing/mochitest/tests/SimpleTest/specialpowersAPI.js
index 77af2d5768d..419d8a9302c 100644
--- a/testing/mochitest/tests/SimpleTest/specialpowersAPI.js
+++ b/testing/mochitest/tests/SimpleTest/specialpowersAPI.js
@@ -676,5 +676,34 @@ SpecialPowersAPI.prototype = {
                    withCaret ? ctx.DRAWWINDOW_DRAW_CARET : 0);
     return el;
   },
+  
+  swapFactoryRegistration: function(cid, contractID, newFactory, oldFactory) {  
+    var componentRegistrar = Components.manager.QueryInterface(Components.interfaces.nsIComponentRegistrar);
+
+    var unregisterFactory = newFactory;
+    var registerFactory = oldFactory;
+    
+    if (cid == null) {
+      if (contractID != null) {
+        cid = componentRegistrar.contractIDToCID(contractID);
+        oldFactory = Components.manager.getClassObject(Components.classes[contractID],
+                                                            Components.interfaces.nsIFactory);
+      } else {
+        return {'error': "trying to register a new contract ID: Missing contractID"};
+      }
+
+      unregisterFactory = oldFactory;
+      registerFactory = newFactory;
+    }
+    componentRegistrar.unregisterFactory(cid,
+                                         unregisterFactory);
+
+    // Restore the original factory.
+    componentRegistrar.registerFactory(cid,
+                                       "",
+                                       contractID,
+                                       registerFactory);
+    return {'cid':cid, 'originalFactory':oldFactory};
+  },
 };
 
diff --git a/toolkit/content/tests/browser/common/mockObjects.js b/toolkit/content/tests/browser/common/mockObjects.js
index 370158db890..4a65e17f9da 100644
--- a/toolkit/content/tests/browser/common/mockObjects.js
+++ b/toolkit/content/tests/browser/common/mockObjects.js
@@ -65,7 +65,6 @@ MockObjectRegisterer.prototype = {
    * to ensure that unregister() is called.
    */
   register: function MOR_register() {
-    netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
     if (this._originalFactory)
       throw new Exception("Invalid object state when calling register()");
 
@@ -79,41 +78,24 @@ MockObjectRegisterer.prototype = {
       }
     };
 
-    var componentRegistrar = Components.manager.QueryInterface(Components.interfaces.nsIComponentRegistrar);
-
-    // Get the component CID.
-    this._cid = componentRegistrar.contractIDToCID(this._contractID);
-
-    // ... and make sure we correctly replace the original factory with the mock one.
-    this._originalFactory = Components.manager.getClassObject(Components.classes[this._contractID],
-                                                              Components.interfaces.nsIFactory);
-
-    componentRegistrar.unregisterFactory(this._cid, this._originalFactory);
-
-    componentRegistrar.registerFactory(this._cid,
-                                       "",
-                                       this._contractID,
-                                       this._mockFactory);
+    var retVal = SpecialPowers.swapFactoryRegistration(this._cid, this._contractID, this._mockFactory, this._originalFactory);
+    if ('error' in retVal) {
+      throw new Exception("ERROR: " + retVal.error);
+    } else {
+      this._cid = retVal.cid;
+      this._originalFactory = retVal.originalFactory;
+    }
   },
 
   /**
    * Restores the original factory.
    */
   unregister: function MOR_unregister() {
-    netscape.security.PrivilegeManager.enablePrivilege("UniversalXPConnect");
     if (!this._originalFactory)
       throw new Exception("Invalid object state when calling unregister()");
 
     // Free references to the mock factory.
-    var componentRegistrar = Components.manager.QueryInterface(Components.interfaces.nsIComponentRegistrar);
-    componentRegistrar.unregisterFactory(this._cid,
-                                         this._mockFactory);
-
-    // Restore the original factory.
-    componentRegistrar.registerFactory(this._cid,
-                                       "",
-                                       this._contractID,
-                                       this._originalFactory);
+    SpecialPowers.swapFactoryRegistration(this._cid, this._contractID, this._mockFactory, this._originalFactory);
 
     // Allow registering a mock factory again later.
     this._cid = null;