Try disabling "Use Hardware Acceleration when available" in Firefox (tools -> options). Helped me out of some damn nasty issues I had a few months back.
I think the feature is fucked up for some video card drivers (had problems even when using the latest nvidia). They better fix it soon before her market goes to the "I LUBS teh datamining" chrome crowd or the "what's this Internetz I keep hearing about" IE folks.