On Thursday, Opera released version 9.51. The new version fixes a few security vulnerabilities and resolves some stability issues. One of the fixes addresses an arbitrary code execution vulnerability that was not previously made public.
Meanwhile, Mozilla released Firefox 2.0.15 with a dozen security fixes, including a few remote-execution vulnerabilities.
Current Firefox 2 users should, however, upgrade to Firefox 3, which includes antimalware protection and other security features.