Add New Toolbar
I find it odd that this extension has to exist at all (well I do know the reasons behind it, but still). This handy tool ports the "Add New Toolbar" button in the Customize toolbar window from Firefox to Thunderbird.
Some people will be pleased to know they can use this to get the "Location" bar that was in Thunderbird 1.5 back into Thunderbird 2.
This functionality is also included in the "Toolbar Buttons" extension. For those that use that extension, there is no need to install this one too.