Firefox 3.5  is based on the Gecko 1.9.1 rendering platform, which has been under development for the past year. Firefox 3.5 offers many changes over the previous version, supporting new web technologies, improving performance and ease of use. Some of the notable features are:

• Available in more than 70 languages. (Get your local version!)
• Support for the HTML5 <video> and <audio> elements including native support for Ogg Theora encoded video and Vorbis encoded audio. (Try it here!)
• Improved tools for controlling your private data, including a Private Browsing Mode.
• Better web application performance using the new TraceMonkey JavaScript engine.
• The ability to share your location with websites using Location Aware Browsing. (Try it here!)
• 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: downloadable fonts, CSS media queries, new transformations and properties, JavaScript query selectors, HTML5 local storage and offline application storage, <canvas> text, ICC profiles, and SVG transforms.

Developers can find out about all the changes and new features at the Mozilla Developer Center.

Download the latest version firefox HERE