Firefox 2.0.0.4 contains a fix for a directory traversal vulnerability
that allowed you to read local files through the resource protocol.

However, the patch only partially fixed the vulnerability on Windows
systems and accidentally circumvents an existing input validation
check.

The net result is that you can still read some local files on Windows
and all user accessible files on Linux/Unix/OS X, with all user
accessible files potentially readable as well on Windows through the
patch regression.

http://larholm.com/2007/06/04/unpatched-input-validation-flaw-in-firefox-2004/ 

Cheers

Thor Larholm