There is a new advisory out that indicates there is a remote denial of service exploit in Firefox 1.5.0.7 and Firefox 2. The original post indicated that there could be a buffer overflow and remote code execution component, but as of 10/31 this has not been verified. This exploit will occur when a specifically crafted webpage tries to create a range object with "createRange". So far it will only make the browser crash.
http://isc.sans.org/ - Full story.

Cheers: