The pwn2own bug that Nils discovered at CanSecWest 2009 and the XSLT vulnerability recently made public by Guido Landi (http://www.securityfocus.com/bid/34235) are both critical issues that can result in malicious code execution.
Both issues have been investigated and fixes have been developed which are now undergoing quality assurance testing. These fixes will be included in the upcoming Firefox 3.0.8 release, due to be released by April 1. You can follow our work in bugzilla.
The pwn2own bug was reported to Mozilla by Nils via the Zero Day Initiative (ZDI). The XSLT issue was discovered on http://www.milw0rm.com/exploits/8285, credited to Guido Landi.