"At this time, we don't have a good estimate for when we'll be releasing Beta 3, as there are some issues remaining which are tricky and complicated, and we want to ensure are fully resolved," said Mike Beltzner, Mozilla's director of Firefox development, in a statement. "We're working on a revised schedule, which should be posted in a few days."
This isn't the first time Firefox 3.1 has been delayed. The Feb. 2 release date for beta 3 was already rescheduled from Jan. 26. And in November, Mozilla announced a third beta to allow the company to conduct more testing.