The second Beta development milestone of Firefox 3.1, codenamed Shiretoko, is now available for download. While it had already started working on Firefox 3.1 Beta 3, Mozilla managed at the end of the past week to deliver the Beta 2 bits of the next iteration of its open source browser. Labeled a public preview release, Firefox 3.1 Beta 2 is designed to enhance web compatibility and speed, as well as take performance to the next level. A taste of Beta 3 is already up for grabs, with Mozilla having debuted work on the next development milestone while it was still wrapping up the Beta 2 build. Following Beta 3, Firefox 3.1 will move into release Candidate (RC) stage.

If until the Beta 2 release Mozilla failed to bring the new TraceMonkey JavaScript engine into the limelight, this is no longer the case. TraceMonkey is now turned on by default in Firefox 3.1 Beta 2, and users no longer have to dig into the browser's configuration in order to enjoy superior JavaScript performance. In addition, the improvements in TraceMonkey have been accompanied by the evolution of the Gecko layout engine, also with the focus on performance.

On the track of Internet Explorer 8, Mozilla now introduces Private Browsing Mode, kicking the privacy capabilities of the open source browser to the next level. Via the Clear Recent History options, users can be extremely selective about what Firefox 3.1 Beta 2 will remember of their browsing session. Available in 54 localized versions, Firefox 3.1 Beta 2 comes to the table with boosted support for <video> and <audio> elements, the W3C Geolocation API, JavaScript query selectors, CSS 2.1 and 3 properties, SVG transforms and offline applications.

In this context, Firefox 3.1 Beta 2 now comes very close to acing the Acid3 Test, which Opera 10.0 Alpha 1 has no problems passing with flying colors, while the same cannot be said about Internet Explorer 8. Still, changes also reverberate on the surface of the open source browser, namely in terms of user experience.

The alterations related to the tab switching and preview behavior, which were made available in previous releases of Firefox 3.1, will be most notable. New Tabbed Browsing capabilities now allow users more flexibility when it comes down to handling tabs, including dragging and dropping items outside of one instance of Firefox in order to make a transition of  the content to a standalone window. Additionally, Firefox 3.1 Beta 2 now provides more information about the updating process, including an estimate of the time remaining. The restore capabilities of Firefox 3.1 have also evolved, with a new session restore dialog box permitting users to select exactly the tabs and windows they want to be restored in the eventuality of a crash.

Firefox 3.1 Beta 2 for Windows is available here.

Firefox 3.1 Beta 2 for Linux is available here.

Firefox 3.1 Beta 2 for Mac OS X is available here.