Firefox 3.5 introduces a number of new features, as well as additional and improved support for a wide variety of web standards
Some of the notable features of Firefox 3.5:
- Available in more than 70 languages.
- Support for the HTML5 and elements including native support for Ogg Theora encoded video and Vorbis encoded audio.
- 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.
- 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, text, ICC profiles, and SVG transforms.
you can find more features listed with visuals on Lifehacker.
Enjoy 
