I would strongly consider filling a bug report because this issue is with the current development version of Firefox. I would check to see that no one else has reported this problem before you.

i have the same problem. im very happy i found someone with the same problem.

Sounds like a problem with the theme that you use and that is not compatible with that version.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).

See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

I have the same problem but found the problem. The "Menu Bar" is hidden by default behind the orange firefox button if you click it and then Customize > Menu Bar click it and it should give you back the min, max, and close buttons

Thanks for the advice, I was able to get 4.0B working in safe mode and eventually determined that 16 out of 21 extensions are incompatible with this version of firefox. Virtually nothing works in this beta version, rendering it pretty much unusable. I checked in bugzilla and did not see anything addressing these problems but given that, so far, almost no extensions work with this beta version I am just going to go on using 3.6.6

A lot of extensions need to be reworked for Firefox 4.0 See http://forums.mozillazine.org/viewtopic.php?f=23&t=1937759

Likewise... the Google toolbar no-longer works, and our own toolbar from Conduit does work but some of the buttons are distorted