Mozilla has released Firefox 3.1 Beta 1, the first preview meant for the general public, but disabled one of its most-touted improvements.

In a posting to its developer center today, the company cited improvements in "performance, Web compatibility and speed" to Firefox and said that it wanted users to focus on testing the core functionality of the open-source browser.

Among the new features the company highlighted are support for the "video" and "audio" HTML tags, a new tab-switching shortcut that mimics an existing Firefox add-on called Ctrl-Tab, and the new geolocation API that uses third-party services to pinpoint the user's location and feed that information to Web sites and services.

Mozilla's Geolocation API has been prominent since last week, when the company's research labs rolled out a new extension, Geode , for Firefox 3.0 that reproduces the feature built into Firefox 3.1. At the time, Mozilla's director of Firefox, Mike Beltzner, argued that the API, though of obvious use in the still-under-development mobile version of Firefox, will also be important on netbooks, the ultralight, less-expensive laptops that are becoming more popular.

But Mozilla did not enable its new TraceMonkey JavaScript engine in Beta 1; it's still switched off by default.

TraceMonkey, which Mozilla began talking up in late August, boosts rendering speeds up to 40 times over those of Firefox 3.0, which relies on an older engine. Mozilla started working on TraceMonkey at the beginning of the summer, and wrapped up enough of the initial work to slide it into the "nightlies," the versions of Firefox that are updated daily for testing and development purpose.

Mozilla officials were not available late Tuesday to explain why they decided to leave TraceMonkey turned off.

Users can, however, enable TraceMonkey themselves by typing "about:config" in the address bar, entering "javascript.options.jit.content" in the Filter field, then setting that to "True" by double-clicking the item. Firefox 3.1 must be restarted for the change to take effect.

At one point, Mozilla had hinted it would roll out just a single beta during the fast-track development of Firefox 3.1, but it recently added a second beta -- and several more weeks to the schedule -- to squeeze in several other features. Only last week did Mozilla settle on what it will drop into Firefox 3.1 Beta 2.

According to Mozilla's current schedule, it will freeze Beta 2's code November 4, with a likely release one to two weeks after that. It has not committed to a ship date for Firefox 3.1, but has said it will shoot for a late-2008 or early-2009 release.

Firefox accounted for 19.5 percent of the browsers used during September, according to Net Applications. Its share that month, however, was down slightly from August.

Firefox 3.1 Beta 1 can be downloaded for Windows, Mac OS X and Linux from Mozilla's site. Not all localized versions are available, however; still missing, for instance, are the Arabic, Greek and Turkish editions.