Until recently, Firefox on my machine used the standard Unity global menu. However, recently the menu is no longer global and, strangely, is centered. See this screenshot:

firefox-globalmenu is installed, the extension is enabled on the Add-ons page, and all other programs work as expected. Furthermore, the menu is as expected in a guest session.

Here are the extensions I have enabled:

• Adblock Plus 2.0.3
• AutoPager 0.7.1.2
• Firebug 1.9.0
• Flagfox 4.1.11
• Global Menu Bar Integration 2.0.2
• InstantFox 2.6.1
• Searchbar Autosizer 1.5.7
• Tab Scope 1.1.3
• Ubuntu Firefox Modifications 1.0.2
• United States English Spellchecker 5.0.1 (frequently fails to check spelling, allowing words like "spekk" and rejecting all contractions such as "can't")
• Unity Integration for Firefox 0.2.4

How can I get the global menu back?

(This is Ubuntu Oneiric [11.10] with Firefox 9.0.1.)

Update

I restarted in safe mode (all add-ons disabled). Here's what I saw (note that the only change is that the menubar is no longer centered):

Next, I renamed ~/.mozilla to try a fresh profile. The problem was cured. However, I consider this to be an unacceptable solution since I have a lot of settings, add-ons, stored data, etc., etc. that would be lost with a fresh profile, only some of which is covered by Firefox Sync. A solution that involves lost data is no solution.

With your old profile, could you simply disable all extensions and see if the problem goes away? (Somewhat like the safe mode you already tried.) Then, re-enable one extension at a time and see. (Obviously, the global menu bar extension shouldn't be disabled.)

If it's just a single extension (instead of some tricky "synergism"), you may be able to pin-point which one this way and then decide if you can live without it or have to endure the novelty of a centered global menu.