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, Google and Microsoft started 2011 with some breaking news! Mozilla is releasing Firefox 4 Beta 9 on January 13. Chrome 9 beta got updated. Some Microsoft is planning to have first release candidate of Internet Explorer 9 by January end!