Hell I knew Mozilla would can the Win64 we would of had it by now as with IE and Opera now offering 64 bit versions and I am pretty sure Windows will eliminate their 32 bit OS's leaving Mozilla out in the cold and they already have in their server OS's. But no worries, there are damned good 64 bit Firefox variants that let me tell you WORK with most extentions and addons. I have been using Waterfox a 64 bit variant and it blows the doors off of Mozilla's 32 bit Windows release. This browser is stable and most of Mozilla's 64 bit developers are flocking to the Waterfox Project.
This is arguable why Mozilla canceled the browser's development since Waterfox developers were far more advanced in producing a browser that supports the extensions and addons. Kudos to the Waterfox Project! Mozilla since it is open source opted to allow third parties to further develop the 64 bit browser as a variant.