The final release of Firefox 4 is available on the Mozilla website. Should be announced on their main page tomorrow.
Windows
http://releases.mozilla.org/pub/mozilla.org/firefox/releases/4.0/win32/en-US/Firefox%20Setup%204.0.exe
Linux
http://releases.mozilla.org/pub/mozilla.org/firefox/releases/4.0/linux-i686/en-US/firefox-4.0.tar.bz2
Mac
http://releases.mozilla.org/pub/mozilla.org/firefox/releases/4.0/mac/en-US/Firefox%204.0.dmg
For anyone with blurry text in Firefox 4, disable hardware acceleration as it's a bug with DirectWrite.