Mozilla has released Firefox 3.1 beta 3, a public preview release intended for "developer testing and feedback".

The third beta for the release features a number of improvements to performance, web compatibility and speed.

These include an improved Private Browsing Mode, featuring a one-click button to "Forget This Site" from the History sidebar, improved performance and ability from Firefox's new TraceMonkey JavaScript engine, and native JSON support.

Support has also been added for a number of new web technologies including HTML video and audio support, geolocation, API, offline application support and CSS improvements.

Mozilla are urging any developers downloading Beta 3 for testing, available now for Windows, Mac OS and Linux, to read the Mozilla Developer Center blog to check out the full list of tweaks they need to test out for feedback.

There's no news on when we can expect to see the finished product, but as the developer's blog speaks of a upcoming Beta 4, it seems it could be some time yet.

We've contacted Mozilla to find out a timescale, and we'll keep you posted.