Firefox 3.1 Beta 2 is the fourth development milestone and second beta release of Firefox 3.1, the next version of the Firefox web browser. While this release is considered to be stable, it is intended for developers and members of our testing community to use for early evaluation and feedback. Users of the latest released version of Firefox should not expect all of their add-ons to work properly with this beta. Firefox 3.1 Beta 2 is based on the Gecko 1.9.1 rendering platform, which has been under development for the past 7 months. Gecko 1.9.1 is an incremental release on the previous version with significant changes to improve web compatibility, performance, and ease of use:

• This beta is now available in 54 languages
• Added a new Private Browsing Mode.
• Added functions to make it easy to clear recent history by time as well as remove all traces of a website.
• New support for web worker threads.
• The new TraceMonkey JavaScript engine is on by default for web content.
• Improvements to the Gecko layout engine, including speculative parsing for faster content rendering.
• Removed the new tab-switching behavior based on feedback from users
• Support for new web technologies such as the and elements, the W3C Geolocation API, JavaScript query selectors, CSS 2.1 and 3 properties, SVG transforms and offline applications. More information.