Mozilla has confirmed that it will release the next major version of Firefox on Tuesday, June 30.

Firefox 3.5 is the first major revision of the popular open-source browser since version 3 landed a little over a year ago, in June of 2008. 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, and adding new features for users.

Firefox 3.5 will also include support for the most widely-used elements of HTML 5, the set of next-generation web standards that allows for offline data access, enhanced web graphics and multimedia playback without plug-ins.

Here is a glimpse of the new features in Firefox 3.5:

• Improved tools for controlling your private data, including a Private Browsing Mode.
• Better performance and stability with the new TraceMonkey JavaScript engine.
• The ability to provide Location Aware Browsing using web standards for geo-location.
• Improvements to the Gecko layout engine, including speculative parsing for faster content rendering.
• Support for new web technologies such as: HTML5 <video> and <audio> elements, downloadable fonts and other new CSS properties, JavaScript query selectors, HTML5 offline data storage for applications, and SVG transforms.

Firefox 3.5 is currently in the post-beta release candidate (RC2) stage. You can grab a preview release here, if you can’t wait until Tuesday for the final release.