Mozilla team is all set to release Firefox 4.0 Beta 11 by early next week. And it is extending its beta branch to Beta 12. Maybe Firefox 4 first Release Candidate(RC) will be delayed for few days.
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.