Mozilla has admitted that Firefox 3.6 and Firefox 4 will miss their slated release dates.

Firefox 3.6 was originally set to launch by the end of December, but despite the release of five betas, Mozilla has been unable to iron out the bugs in time.
The browser has now been pushed back until the first quarter 2010, according to the Mozilla Wiki.
Firefox 4 – which Mozilla planned to release in October or November 2010 – has also been hit by the delay. The browser has now been pushed back until “late 2010 or early 2011.”
The first beta will make its appearance in summer.
The delays follow a prolonged battle to get Firefox 3.5 out of the door. Bugs in the TraceMonkey rendering engine delayed the browser for over six months and ultimately forced the company to bump the version number from 3.1 to 3.5.
Firefox 3.6 will bring improved JavaScript performance and start-up times, support for the HTML video tag and accelerometers, and alerts regarding out-of-date plugins.
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