Comment 4 for bug 1124870

Yep, this is intentional. The menubar addon broke with a recent API change, and I'm no longer going to spend time updating it (especially as it's becoming more difficult to support a binary addon, and each fix just feels like another sticking plaster). So it's disabled now. The plan is to support this natively in Firefox instead (hence the patch I've just attached to the bugzilla)