Mozilla announced Firefox 3.1 has been delayed to the second quarter of this year or later, mainly due to many bugs in TraceMonkey. The third beta version of Firefox 3.1 will be released this week, and a fourth beta is expected by mid-April.
The decision was not unexpected. Last weekend, Shaver said that bugs in TraceMonkey had slowed the development pace, which in turn had kicked the browser's release into next quarter . He also said that developers were considering a fourth beta.