Mozilla fans can now play with the anticipated speedier JavaScript engine in the first beta for Firefox 3.1, as well as explore improvements to the Smart Location Bar and a slick interface for hotkey tab switching. Now available for Windows, Mac, and Linux users, the new JavaScript engine, called TraceMonkey, is not turned on by default.

The latest Firefox beta introduces a visual tab switcher and rolls in the Geode geolocator plug-in. (Credit: CNET Networks)

To activate it, type "about:config" into the Smart Bar, then type "javascript.options.jit.content" into the filter. Double-click on the preference listed to change the boolean setting from "false" to "true." Close the window and you should notice an immediate improvement to the JavaScript rendering speed.

Don't take my word for it, though. Using the SunSpider JavaScript Benchmark test, Firefox 3.1 beta 1 completed the test in 2787.6 milliseconds--about twice as fast as the current stable release, Firefox 3.0.3, which clocked in at 5446.6 ms.

Using CTRL+Tab to jump between open tabs now has graphic overlay, much like the Windows Vista ALT+Tab program switcher. The Geode geolocator plug-in has been rolled into FF3.1. The Geode drop-down worked for me, but it wasn't always able to find my location.

You can now restrict searches in the Awesome Smart Bar using special characters such as "+" and "#". These and other aspects of the character restrictions are customizable through about:config.

Two much-anticipated features did not make it into this beta. Private Browsing, Mozilla's answer to Google Chrome's Incognito, and enhanced session management features were not available in this beta.

I found that several of my plug-ins were not compatible with the new tab switcher, so I just disabled all of them. Using a plug-in to force forward-compatibility in other plug-ins can lead to instability and crashes, arguably even more so because this is a beta. However, if you're interested in getting the fastest version of Firefox that we've seen to date, Firefox 3.1 beta 1 is going to deliver the goods.

You can read the full list of changes here.