FIREFOX - really bad exploit with PoC code out there.
 

Advisory: http://www.frsirt.com/english/advisories/2005/0493

Proof of Concept: http://www.frsirt.com/exploits/20050507.firefox0day.php



The firefox trunk builds are amazing though (and not vulnerable to this) ... lots of new features & huge performance increase. Not sure if the general public should be running them though... I'll be going back to normal releases when this is properly fixed.