If you're already running a previous build of Firefox 4 you should see an automatic update starting tomorrow. Alternatively, you can download the final build directly for Windows, Mac OS X, and Linux 32-bit/64-bit. The final version supports 83 languages.
Mozilla is letting users update Firefox versions 3.5 and 3.6 to 4.0 without the need to navigate to a download page. Firefox 4.0 was supposed to be released tomorrow, and while the download links are up, we expect that the official launch will be announced in the next 24 hours. For more information on what's changed throughout the development of version 4.0, check out the release notes.
Mozilla was originally planning on having Firefox 4 out by the end of last year, but it has had to delay the release multiple times. The company has fixed more than 7,000 bugs in the 12 betas and a few more in the two RC builds.
Mozilla has been struggling to get Firefox 4.0 out the door. As a result, the company has announced that in 2011, not only will we see Firefox 4.0, but we will also see Firefox 5.0, Firefox 6.0, and Firefox 7.0. The first 5.0 builds are already in the making; the next version is targeted for a late June 2011 release.