I just ryed the exploit on too of my machines, one 2Ghz Debian machine and an old PII Gentoo,
my browser where not patched and on both machines i got a very high cpu load, i did not even got to the point to click the butten which rins the eval shell code, so i guess i'm save without patched
Firefox, i'm not sure but all i know about heap overflows is that they don't work on every machine the same
way and that it's difficult to exploit them anyway.