Mozilla's Firefox browser does not lead Microsoft's Internet Explorer in market share, but it does lead in other ways. The new 3.5 version of Firefox introduced last week offers support for the latest standards, including HTML 5, XHTML, and SVG graphics -- all of which stock installs of Internet Explorer 8 do not support.
However, Mozilla does trail Internet Explorer 8 in one respect -- Mozilla has not offered an official 64-bit version of its software. One developer is working to catch Mozilla up, though. Since 2008 a contributor who goes by the screen name Makoto has ported Firefox 3.0, and now 3.5 to 64-bit editions. He has announced recently that he plans to contribute the 64-bit versions for 3.6 and up, which may mean that Firefox will at last get an official 64-bit build.
Advantages of the transition to 64-bit include faster speeds on pages using encryption, fast-call type function calls, and more efficient memory mapping of large files. Initial benchmarks from the 64-bit build show impressive gains in certain applications.
A notable downside of the patch for Firefox 3.5 is that it breaks Mozilla's plug-in system, which relies on a 32-bit architecture. However, Mozilla has talked recently of adding official 64-bit support in the near future, so this will likely be addressed shortly.
Google's Chrome also is not offered in 64-bit versions. Apple's Safari 4 browser is offered in a 64-bit version (and is the first Safari browser to add official 64-bit support). Opera is offered in 64-bit for Linux and OpenBSD operating systems, but is only offered in 32-bit form for Windows. Within about 4-5 years all of these are expected to jump to 64-bit as the next version of Windows (after Windows 7) is expected to only be offered in 64-bit form, though legacy support for 32-bit software will almost surely be included.
Anyone who wants to take 64-bit Firefox 3.5 out for a spin is suggested to back up their profile, as the build will use the same profile as your current installation. It should also be noted that the build only works with 64-bit operating systems such as those based on the Windows x64 platform, like the 64-bit build of Windows 7 Release Candidate.