64-bit version "Firefox" and "Thunderbird"
It is "Firefox" and "Thunderbird" which remodeled the code for the 64-bit version.
Mozilla for Windows x64 platform: Download
Most extensions seem to work, but the plug-in system is bad.
Here is a build method for running on Windows XP 64-bit version.
Mozilla for Windows x64 platform: How to Build Mozilla for Win 64
in Software, Posted by darkhorse_log