Firefox doesnot have separate version for 64bit but the current version works fine with both 32 and 64bit

• getfirefox.com

To be more clearer...

Mozilla has yet to make a official 64-bit version of Firefox for 64-bit Windows Vista/7 and the earliest that may happen is Firefox 12.0.

Firefox 32-bit does work on 64-bit Windows Vista/7. You also need the 32-bit browser plugins.

http://www.mozilla.org/en-US/firefox/9.0.1/system-requirements/

Windows
Operating Systems

   Windows 2000
   Windows XP
   Windows Server 2003
   Windows Vista
   Windows 7

Please note that while the 32-bit and 64-bit versions of Windows Vista and Windows 7 can be used to run Firefox 9, only 32-bit builds of Firefox 9 are supported at this time.