12 others appear to have these issues and yet no response from anyone!? Anybody have any idea what might be going on here or should I just give up on FF 4 completely?

Try:

• http://kb.mozillazine.org/Corrupt_localstore.rdf

Hide the Menu Bar to make the orange Firefox button appear.

If you need to access the hidden Menu bar then press F10 or hold down the Alt key to make the Menu Bar appear temporarily.

You can place the Tab Bar on top.

• View > Toolbars : [ ] Menu Bar
• View > Toolbars : [X] Tab onTop

I have solved this problem on my system; so maybe this is the issue for others also. The problem was caused by a conflict with the IDM add-on. Although this add-on appeared to be updated it actually wasn't. Full details of how to resolve the issue are here http://www.internetdownloadmanager.com/support/firefox_integration.html Installing the new add-on IDM CC 7.2.8 has solved all the issues noted above.

Re-integration of IDM CC 7.2.8 didn't work for me. The "Open new tab" (+ button) is still at the far right side of the top bar. I noticed that if I run Firefox4 with its desktop icon I have this problem, BUT when I click CTRL+N from within the Firefox Window - the newly opened window has it's "+" button right where it belongs: right to the last opened tab. So it looks like simple CTRL+N solves this problem. It seems that IDM CC 7.2.8 needs to be loaded into memory before the new Firefox window appears and it's all OK. Can I somehow load this add-on BEFORE the creation of the Firefox window (or delay Firefox window appearance or something like that)?

P.S. It's funny that this problems manifests only in WinXP Pro, in Windows7 IDM add-on doesn't seem to cause any problems whatsoever.