I've been playing a little with compiz today. I don't see any connection between compiz plugins and iceweasel. First I wanted to open iceweasel window on another workspace, it didn't work. I relogged and it work. Now another time I want to open it doesn't respond. It just loads but nothing happen. I can't open any new iceweasels until I kill firefox-bin process. I disabled all the plugins I enabled today. Even replaced compiz with metacity but it doesn't work. It's like it won't let have another firefox-bin process. And when I close iceweasel the process isn't killed, I have to do it myself. I don't see how it's related to compiz, but this is the only thing I done with the system today.

Edit: I think it happened even before configuring compiz. I posted a thread here couple hours ago and I wasn't able to open "click here to find similar threads" window.
Edit2: I got it, it was caused by firebug extension which didn't work at all.