Mozilla recently officially released Firefox 3.5, the first significant upgrade to Firefox since version 3.0 was released a year ago.

Since then, the browser market has changed substantially. Microsoft released Internet Explorer 8. Google released Chrome. And Apple released Safari 4.

And those companies see their browsers as critical to their emerging Web application strategies. As Google VP of engineering Vic Gundotra put it at his company's Web developer conference, "The Web has won."

The Web's victory makes the Web browser all the more important. Web browsers must be fast and reliable at the very least if consumers are to have a positive experience using browser-based online applications.

Firefox 3.5 is in some ways a catch-up project. Version 3.0 suffered when compared to Google Chrome and Apple's Safari in terms of speed. It was also slow to be delivered: Back when it was called Firefox 3.1, it was supposed to be released at the end of 2008.

Mike Beltzner, Mozilla's director of Firefox, has acknowledged the competitiveness of the market but welcomes competition as a driver of innovation. And there's some truth to that, given that both Firefox and Chrome are open-source projects. The next version of Firefox will be getting process protection, courtesy of libraries developed for Google Chrome.

Thankfully for Mozilla, Firefox 3.5 is competitive with other modern browsers in terms of speed and memory usage. Mozilla claims it is two times faster than Firefox 3 and ten times faster than Firefox 2.

Some of the speed improvement comes from the new TraceMonkey JavaScript Engine. A feature called Web Worker Threads, which brings multithreading support to Web applications, also helps speed things up.

Firefox 3.5 includes Private Browsing, a feature pioneered by other browsers that keeps Web site visits from being recorded on the client side. It also includes Location Aware Browsing, which is a way to share user location data with Web sites and services.

Firefox 3.5 also introduces new HTML 5 features like support for open video and audio file formats. With version 3.5, users can play Ogg Theora videos without an external plug-in, like Adobe's Flash Player plug-in. And with HTML 5 support, Web developers can access video data programmatically, using JavaScript. This will allow a variety of new online applications that haven't been possible previously using only browser technology.

Firefox 3.5 remains the most customizable browser on the market with over 6,000 add-ons, support for browser themes, and personalization projects like Personas.

Whether it will remain the dominant alternative to Microsoft Internet Explorer, remains to be seen. Firefox has seen its global market share grow every month for several years now. Rest assured that the Mozilla community will be working to continue that trend.