Mozilla is making plans for 64-bit Firefox browser

If you want a 64-bit build of Firefox right now, you might want to check out Waterfox, which I've been happily using for a while on Windows 7:

https://www.waterfoxproject.org

I moved from Firefox to Waterfox during a period where Firefox was frequently crashing on me. Waterfox seems to be more stable if you have lots and lots of tabs open.