Please note: Firefox 3.5 Beta 4 is a public preview release intended for developer testing and community feedback. It includes many new features as well as improvements to performance, web compatibility, and speed. We recommend that you read the release notes and known issues before installing this beta.

Firefox 3.5 (formerly known as Firefox 3.1) Beta 4 is now available for download. This milestone is focused on testing the core functionality provided by many new features and changes to the platform scheduled for Firefox 3.5. Ongoing planning for Firefox 3.5 can be followed at the Firefox 3.5 Planning Center, as well as in mozilla.dev.planning and on irc.mozilla.org in #shiretoko.

New features and changes in this milestone that require feedback include:

• This beta is now available in 70 languages – get your local version.
• Improved tools for controlling your private data, including a Private Browsing Mode.
• Better performance and stability with the new TraceMonkey JavaScript engine.
• The ability to provide Location Aware Browsing using web standards for geolocation.
• Support for native JSON, and web worker threads.
• Improvements to the Gecko layout engine, including speculative parsing for faster content rendering.
• Support for new web technologies such as: HTML5 <video> and <audio> elements, downloadable fonts and other new CSS properties, JavaScript query selectors, HTML5 offline data storage for applications, and SVG transforms.

Source: Mozilla Developers News