The custom host file method works in Firefox.
Windows has a host file and you can add any site you want to it.
The host file is found in C windows system32 drivers etc.
Another great feature of the HOSTS file is that it is a two-way file, meaning if some parasite does get into your system (usually bundled with other products) the culprit cannot get out (call home) as long as the necessary entries exist. Hosts File : Use in Windows 7 / Vista