Mozilla has updated Firefox 2011 roadmap and it seems Mozilla is planning to release Firefox 4.0, 5.0, 6.0 and 7.0 versions in 2011.

Here is what the roadmap mentions:

* Ship Firefox 4, 5, 6 and 7 in the 2011 calendar year
* Support new operating systems and hardware
* Plan and architect for a future of a common platform on which the desktop and mobile products will be built and run Web Apps

Plans for Firefox Front End:

* Simple Sharing
* Animations in the user interface
* 50 high priority polish issues for common taskflows
* Asynchronous Places
* Account Manager
* Remove Smart Search functionality from Bookmark Manager
* Electrolysis
* Web Application Install/Uninstall Support
* Process-per-tab to mitigate effects of crashes

Firefox 5.0 Scheduled Features Set:

* Account Manager
* Simple Sharing UI
* UI Animation
* 64 Bit on Windows

Firefox 6.0 Scheduled Features Set:

* Web Applications
* FasterCache
* OSX 10.7
* JS Optimizations

Firefox 7.0 Scheduled Features Set:

* e10s? deXBLification?


full details https://wiki.mozilla.org/Firefox/Roadmap