As you are no doubt aware, a couple of pretty nasty security defects have been found in the latest FireFox bits that allow remote code execution.

The IE team has made some very gracious comments here about the issue.

The official word about the bugs is from the Mozilla folks http://www.mozilla.org/security/announce/mfsa2005-42.html, and Secunia has marked this Extremely Critical http://secunia.com/advisories/15292/.