I'm using Firefox 23.0 on Ubuntu 12.04 LTS 64-bit. I'm having this annoying problem that when I select view-->customize and drag the dropdown bookmarks menu to the bookmarks toolbar, it disappears the moment I quit customize.

I've started Firefox in safemode to make sure it's not an add-on problem, purged and reinstalled it, created new user profile (moved .mozilla directory) and purged ubufox; none of these things helped.

The Bookmarks Toolbar is enabled. I want to put the drop-down bookmark menu (it's a button) on that toolbar. I go to customize and drag it onto the toolbar, but the moment I click "done" it disappears. If I go to customize again I still see it on the toolbar, but the moment I quite customize it disappears again.