X64 Build

From Mozilla x86-64

What is x64 build

Although Linux, Mac OS X and Windows are released for x86-64 OS platform, officially build by mozilla.org / mozilla.com is still for x86 only. This is native 64 bit coded mozilla (Firefox).


  • Sun Microsystems provides x64 assembler code for RC4 and MPI. It will be improved on SSL connection speeds. (Sun uses NSS library for their server platform that its original is Netscape.)
  • x64 platform has additional 8 registers and fast-call type function call (Windows is 4 registers and Unix is 6 registers).


  • All plugins are 32-bit dynamic library. So it cannot use on 64-bit Mozilla. About available plugins, see Firefox:Plugins.
  • Currently, TraceMonkey (JavaScript JIT) doesn't works on 3.5 and 3.6. This JIT is turned on by 3.7.

Known Issue

  • Mozilla platform cannot use over 4GB memory area as 1 memory block. Because many code uses PRUint32 and PRInt32 instead of PRSize and has 2GB limit condition code.


See x64 Performance on Linux and Windows.

Tracking bug of Windows x64 in Mozilla's Bugzilla

  • 471090 - [meta] Windows x64 build tracking bug