Mozilla has released Firefox 4 Beta 10 and its available for download. New plan is out regarding Beta 11 and Beta 12. We may get Beta 12 before first release candidate of Firefox 4.0.
Mozilla has planned to release Firefox 4 beta 10 by January 24 and beta 11 by 31. So there will be two more betas before release candidate(RC) which is planned to release in early February.
Mozilla is planning to ship release candidate(RC) of Firefox 4.0 by early February and final version by end of February. And its confirmed that we will see Beta 10 soon.