After several delays due to show-stopping bugs in its new JavaScript engine TraceMonkey, Firefox released the third beta version of Firefox 3.1, aka Shiretoko. Starting Thursday, the last beta before the version number changes to 3.5 was released to developers and testers for evaluation and feedback.

The third beta offers improved performance and stability with the new TraceMonkey JavaScript engine, new native support for the JSON (JavaScript Object Notation), and support for new web technologies such as the and elements, the W3C Geolocation API, JavaScript query selectors, CSS 2.1 and 3 properties, SVG transforms and offline applications.

The new version of the software also includes a unique feature called "Forget About This Site," which allows users to selectively tell the web browser to omit specific web sites that have already been visited in the History sidebar, which is an improvement to the Private Browsing Tools that Mozilla premiered at the end of 2008.

Available for download in 64 languages and for Windows, Macintosh, and Linux operating systems, Mozilla warned users that the beta is a preliminary version for testing purposes.

"Firefox 3.1 Beta 3 is a public preview release intended for developer testing and community feedback," Mike Beltzner, director of Firefox, said in an entry to the company's developer blog. On the download page, it got even more specific: "This is pre-release software: you may encounter compatibility problems with some Web sites and add-ons."