Mozilla fans are free to try out the faster JavaScript engine in the first beta for Firefox 3.1, and 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.
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.
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.
A complete list of changes can be found here: release notes.