The latest version of Firefox to come out is version 18.104.22.168, which was released on July 30, 2007. I am not sure why but the auto update didn't work and I had to install it manually.
The following security issues have been fixed:
MFSA 2007-27 Unescaped URIs passed to external programs
MFSA 2007-26 Privilege escalation through chrome-loaded about:blank windows