Direct and to the point. Flash 10 is utter bullshit. Its not worth it. It will mess up Firefox and make it crash, stutter, use up massive amounts of RAM (had over 500+ MB of RAM being used with a few flash pages open) and other such un-fun stuff.
Get rid of Flash 10, now. Uninstall it and get Flash 9 instead. Don’t upgrade Flash and flip the finger to Adobe if they try to convince you otherwise.
I’m just so incredibly and utterly pissed at them for ruining things and making Firefox run so poorly with their shit-ass plugin.