Wow, just tried that and it is surprisingly fast. Wasn't expecting to notice a difference, but I did. Running on a Windows 8 x64, SSD drive, 1.7GHz i7.
...for Windows Operating Systems.
Firefox is natively 64bit on Linux and OSX already.
So? I replied to a comment about Pale Moon (not Firefox, which I'm obviously using), so you might wanna take your downvote back.
From their website: "A custom-built and optimized Firefox-based browser for Windows"