Despite what we reported last week, there was an unexpected (and unannounced) RC2 released on March 18. The final release build seems to have followed quickly after on Saturday, March 19. The official launch of Firefox 4 is due tomorrow.
For more information about Firefox 4, check our complete guide. We also have a fine selection of Firefox 4's finest restartless add-ons.
Update: Mozilla has asked us to say that this might not turn out to be the actual final build. It's still going through QA right now, and something might come up. Don't worry though: your browser will automatically update if a new build is released.
There are also some exciting goodies planned for tomorrow, and Mozilla doesn't want us to satisfy your Firefox 4 hunger just yet. Basically, if you want to enjoy the 'true Firefox 4' experience (including the pretty first-run splash screen), you should hold off installing until it's released tomorrow.
[thanks to everyone who sent this in!]