Firefox officially don't have 64-bit version, but 32bit support 64bit also

Download beta firefox

• http://www.mozilla.org/en-US/firefox/all-beta.html

64bit version of firefox

• http://www.waterfoxproject.org/

Officially, Mozilla does have a 64-bit version and it is called NIGHTLY and I use Nightly (64), Aurora (32), and Firefox (32). I did find how to download the beta version of Firefox 22.0 which is the version I am using right now to reply to your message.

Of all the versions Mozilla offers for Windows, Mac OSX and Linux the Win64 nightlies are the only Not officially supported builds as they are mainly for to catch breakage as it is possible to break Win64 without affecting the Win32 builds.

These Win64 builds are Tier-3 builds when the officially supported builds which includes releases are tier-1 and therefore if if there are server or build issues (for Win64 Nightly) it is not a priority to get them working right away.

Note that the Nightly development channel also gets checkins pretty much everyday and gets a update that day as a result with sometimes the occasional respin. This can make it vary in stability day by day as the May 24 build was crash prone for many testers for example.