Minor fix for Firefox 3.6

TMT users who are using Firefox 3.6 may notice an error message ('JavaScript component does not have a method named: "onBeforeItemRemoved") in their error console. If you wish to remove this error, please install this update.

The update is optional since it will not affect the normal usage of TMT.

Technical Information (For developers):
In FF3.6, a new function onBeforeItemRemoved is added in nsINavBookmarkObserver. Add-ons that use this observer may generate this error.