Does this happen only in Firefox?
Is it a specific game or all flash games/animations?
Do you think it maybe overheating?
I suggest you download Speedfan and tell us the Idle temps and the temps when you're browsing/gaming.
It only starts in Firefox, but progresses to freeze most programs. It seems to be all Flash, both games and the animations, though Flash being the reason it crashes, is only an estimated guess as that seems to be when it freezes.
Running speed fan I get:
HD0: 47C
Temp1:51C
Core:43C
I very much doubt that overheating is the problem as the freeze comes as soon as I run flash, not in the middle of running it.