When I have a Flash plugin misbehaving, I can easily find it with ps -axf. However, killing it won't necessarily be enough; Opera's plugin handler hangs until Opera is restarted even though the errant plugin is no more. I dunno if FF would behave better in that regard.

GNOME's System Monitor shows the same level of information as ps, BTW.

If it turns out to be Flash, you should go looking for an update. You are running Flash 10, aren't you? Version 10 under Linux is *much* better than 9. I don't have crashy-flashy under 10, not even in 64-bit.

Wade.