I'm not sure if its a common occurance for other users, but since the 'hardware accelerated support' with Firefox 4 release, firefox seems to regularly cause my graphics card (Nvidea GT320M) on my laptop to 'stop responding' for a few seconds every so often, usually when I have flash websites such as youtube open. It isn't a huge deal since it restarts working again after a few seconds of a black screen, but its annoying non-the-less.

An example of such: earlier today i started up firefox 4, and when it was loading the tabs, the screen turned black, and when the screen came back on, pop up in the windows task bar told me that the graphics card had stoped responding but successfully recovered. Not the first time, but becoming a more regular occurrence.