The Mozilla Group has released Firefox 18.104.22.168 for Linux, Windows and Mac OS X that fixes several security issues, two labelled critical.
The release notes for this version cite the fixes. All users of previous versions are urged to upgrade.
The listed fixes are as follows:
The Firefox 2 page has the latest version. Mozilla has released a beta of Firefox 3 for testing, but for those users who are sticking with the official release 2 version, the current fix is essential.