Mozilla introduced Firefox 3.5 RC1, you can download it over here. This version has support for new web technologies, improved performance, and new features.
This beta is now available in more than 70 languages - get your local version.
Improved tools for controlling your private data, including a Private Browsing Mode.
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.