I had the same issue after installing FF4B1 and for me there was an easy solution to the problem. I don't know if this will work for you (but I hope it will). It seems FF4 was loading an incompatible theme from my FF profile, the solution was: open FF3 and change to the default theme, close FF3 and then open FF4 and hopefully FF4 will load it's default theme with the nice new UI.

Simon's solution worked. I was using an incompatible theme apparently. Running on default right now and everything is A-OK. Thanks!

You guys shouldn't be using the same Firefox Profile with two different versions of Firefox. That is just asking for problems. https://support.mozilla.com/en-US/kb/Profiles

I had the same problem, but on a new install (on a new Win 7 laptop). I was not using an old profile. I tried installing a new theme, (Walnut 2), but this did not help. However, reverting back to the default again has fixed the buttons.

I don't know if this is related, but I also do not get a menu if I right click in the top bar. This had been suggested as an alternative way to minimise the window. That still doesn't work. (It works in Thunderbird.)

Okay, or rather not. The problem has reappeared! After re-sorting my task bar, the Firefox top bar went black and lost the buttons. Maximise, (by double clicking the top bar), also didn't work. All tabs other than current have dark grey backgrounds. Maybe associated, maybe not, the tabs were showing underlying text through them from shortly before the problem reasserted itself. That is clear text, not blurred as normal for Win 7. This time re-enabling the Walnut 2 theme has fixed it.

If no-one responds soon saying problem has a known fix, (not work rounf), I am heading for Bugzilla.

mcab,

Please start a new thread (or go to the MozillaZine Builds forum) - the version number in the "topic" is very old. And if you are still using 4.0b1 you should update to the latest 4.0 Beta6 version.