Faster JS Processing: Firefox 3.5 includes the new TraceMonkey JavaScript engine, which Mozilla says makes it deliver unprecedented performance with today’s complex Web applications. As Mozilla claims it to be, Firefox 3.5 is more than two times faster than Firefox 3 and ten times faster than Firefox 2.

Also, With a new management function in place, Firefox keeps memory usage under control. The XPCOM cycle collector continuously cleans up unused memory.

With Firefox 3.5, users can enjoy video and audio content from within their browser, without the need for any plug-ins. Web developers can embed audio and video into Web pages in open format Ogg Theora, courtesy a new feature of HTML 5. Mozilla claims that it’s the first to integrate this feature directly into the browser like playing music and video files..

Firefox 3.5 includes features designed to protect users’ privacy online and provide greater control over their personal data. With Firefox 3.5 users can have their browser history never record visits to a particular site. Also, FF 3.5 has support for many new languages.
Location Aware Browsing aims to save users time by allowing websites to know where they are located. If a user chooses to share his location with a website, it can use that information to find nearby points of interest and return additional, useful data like maps of the area. This is an optional feature.