Firefox 3 Beta 5 is a developer preview release of Mozilla's next generation Firefox browser and is being made available for testing purposes only.
These beta releases are targeted to Web developers and our testing community to gain feedback before advancing to the next stage in the release process.
The final version of Firefox 3 will be released when we qualify the product as fully ready for our users. Users of the latest released version of Firefox should not expect their add-ons to work properly with this beta.
Please see below for an extensive list of features and enhancements found in Firefox 3 Beta 5, as well as known issues and frequently asked questions. As always, we appreciate your feedback either through this feedback form or by filing a bug in Bugzilla.
What's New in Firefox 3
Firefox 3 is based on the Gecko 1.9 Web rendering platform, which has been under development for the past 32 months. Building on the previous release, Gecko 1.9 has more than 12,000 updates including some major re-architecting to provide improved performance, stability, rendering correctness, and code simplification and sustainability. Firefox 3 has been built on top of this new platform resulting in a more secure, easier to use, more personal product with a lot more under the hood to offer website and Firefox add-on developers.
Firefox 3 Beta 5 includes more than 750 changes from the previous beta, improving stability and web compatibility, providing platform and user interface enhancements, and resulting in the fastest Firefox ever. Many of these improvements were based on community feedback from the previous beta.
source : en-us.www.mozilla.com