Mozilla has already confirmed the release of Firefox 4 final build on 22nd March but if you can’t wait more you can directly download the Firefox 4 final build from Mozilla FTP servers now.
Firefox 4 is one of the most awaited browsers from last one year with more than 12 betas and 2 RCs released.
Once the Firefox 4 officially announce you will be able to update your Firefox directly by visiting Help Menu > Check for Updates.
Firefox 4.0 will ship in 80 languages for Windows, Mac OS X, and Linux.
NOTE: There is no confirmation whether this available Firefox 4 final version via FTP servers is the confirmed final build, it is yet to be announced officially.
Download Firefox 4 for Windows
Download Firefox 4 for Mac OS X
Download Firefox 4 for Linux (x86, x64)