Much like Firefox 3.5.17 and 3.6.14, Firefox 4 Beta 12 has been delayed. Currently there are five bugs holding back the Beta 12 release. Of these five, one is ‘major,’ two are ‘critical’ and three are ‘normal’. Bottom line, barring some miracle does not look like Firefox 4 is going to be released this month. Especially since Mozilla is “reserving the right’ to have a Beta 13 (if needed) release prior to moving to the Release Candidate builds.
Source: ZDNet