Mozilla has officially announced its fourth development milestone and the second Beta release of Firefox 3.1, the upcoming version of the Firefox web browser for Macintosh, Windows, and Linux. While Mac users get pretty much everything else found on other platforms, one bug still clings onto PPC processors, the release notes show.

“While this release is considered to be stable, it is intended for developers and members of our testing community to use for early evaluation and feedback,” Mozilla says. “Users of the latest released version of Firefox should not expect all of their add-ons to work properly with this beta,” the non-profit organization notes.

As avid Firefox users should already know, version 3.1 Beta 2 is based on the Gecko 1.9.1 rendering platform, which has been under development at Mozilla for the past 7 months. Mozilla describes Gecko 1.9.1 as “an incremental release on the previous version with significant changes to improve web compatibility, performance, and ease of use.” Some feature highlights of this release include the following:

- added a new Private Browsing Mode;

- added functions to make it easy to clear recent history by time, as well as remove all traces of a website;

- the new TraceMonkey JavaScript engine is on by default for web content;

- improvements to the Gecko layout engine, including speculative parsing for faster content rendering;

- support for new web technologies such as the <video> and <audio> elements, the W3C Geolocation API, JavaScript query selectors, CSS 2.1 and 3 properties, SVG transforms and offline applications.

Also, Firefox is now localized in a total of 54 languages, according to the changelog, while new support for web worker threads has also been included. Furthermore, perhaps just as important, Mozilla has decided to remove the new tab-switching behavior upon users' requests.

Last week we got a chance to sit down and talk to the President of Mozilla Europe, Tristan Nitot. Since many Mac owners use Firefox to surf, we were anxious to learn when Mozilla was planning to release Firefox 3.1 Release Candidate. Mr. Nitot couldn't put his finger on the exact date, and just estimated that it would be around “the first half of next year.” He did add that they were “this close to releasing a beta 2 for 3.1,” the version he was using on his MacBook at the time of the interview. “I've been using it for a week now and not a single crash,” he gladly told us. For our part, we've been constantly using the 3.1 beta 2 on Macs since its official debut yestersay, and it's solid as a rock.

“For the first time, we have this thing called TraceMonkey, which is a javascript Just-in-Time-compiler, which is similar to Google's V8 engine, or Safari's Squirelfish Extreme,” Nitot added. Thanks to TraceMonkey, “Firefox and Safari will come with some impressive javascript capabilities, while Opera and IE won't have it,” he revealed.

Listed under Known Issues on Macs, viewing an Ogg video, displayed in a <video> tag, causes a hang, according to Mozilla. This is said to occur only on PPC Macs. To download the latest Beta or stable version of Firefox for Mac, use the link below. Let us know if you encounter any bugs or features you've been waiting for to arrive.

Download Firefox 3.1 Beta 2 / 3.0.4 / 2.0.0.18 for Mac (Free)