It isn't a bug in iceweasel, actual it is a bug in xorg-server, first reported on 31 Mar 2012:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=666468The bug is triggered by libcairo, and first come visible on ATI Cards.
Unfortunately the fix for ATI move the bug to the nouveau driver.
Other Distros (manly ubuntu) aren’t bitten by this bug, because they ship a patched version of libcairo, were they switch of the related functions in cairo. I didn't believe that this is the right workaround, because cairo didn't do it wrong, it is xorg related, so the workaround to use a nouveau.conf and switch off acceleration in the "Xorg-driver" is closer to the real Bug. Well it isn't a solution to use a nouveau.conf, but it is somewhat clearer, then to patch a library for disable a function, which do it right, but trigger a bug in a other "library".