very weird
my firefox3 + f8-flashplugin10 does not hang. each time I load a page containing some flash videos, it just stops responding for couple of seconds, then everything goes fine. This works after a fresh install of the whole system.
I don't know what's going on there... some time ago I just couldn't get firefox3 + f8-flashplugin10 work together. If it worked, it had no sound... or just like you reported, it crashed...