I've had the same issue but I've solved it. What you need to do is for a temporary fix is press "F11" twice, or for the permanent fix, do the following, go into the Compiz Settings Manager, and find "Windows Decorations" add the following line to "Decoration Windows":
Code:
(any) | class=Firefox
Once you've done that, close out CCSM, then open CCSM back up again, then change that to:
Then that should solve the problem, it worked flawlessly. If that doesn't work you can always revert back to metacity:
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