Mozilla announced it will be releasing the final version of Firefox 4 on 22 March 2011, barring any nasty bugs in their final tests.

Firefox 4 RC1 has received a very warm welcome; it's time to make a decision to ship. As of now, there are no known issues that would stop us from shipping RC1 as final. At the conclusion of our regular 11:30AM triage session on Wednesday, March 16th, release drivers will decide whether to ship RC1 as Firefox 4.

If at any time we discover issues that would block final release, we would issue an RC2 as soon as possible, reset the ship date, and communicate to everyone,
And good news to XP users, Mozilla execs took the opportunity to point out that Firefox 4 DOES indeed support Windows XP, unlike Microsoft's own Internet Explorer 9 which was released yesterday!