IdOp, maybe it's just me, but my FF 4 looks remarkably like FF 3.6. I have normal buttons, and a normal menu bar at the top (File, Edit, etc.), and I can customize the buttons like before.
Oh, and yes:
I installed it using a regular
portmaster upgrade of the
www/firefox port on FreeBSD, and re-used the existing
~/.mozilla directory. No other things were tweaked.