The second beta of Firefox 3.1 has arrived with a new JavaScript engine, data security mode and web worker threads.

Mozilla Foundation just released the second preview of its upcoming Firefox 3.1, code named Shiretoko (Japanese for "end of the earth"). It serves primarily for testing the newly introduced features and enhancements.

With its new Private Browsing mode (lovingly called Porn Mode by some), Firefox no longer stores your browser history so that you can remove all traces of your surfing. You can also do a more targeted cleanup of your cookies, for example, by removing the last hour's worth or over a particular timeframe.

The Firefox beta also provides a quicker processing of JavaScript code through the TraceMonkey engine already introduced in October. Same goes for the Gecko layout engine, now available in version 1.9.1. Its faster rendering time is partially due to its use of speculative parsing.

Web worker threads are also supported for the first time. Still part of a yet-to-be-released specification, web worker threads allow the browser to do computation-intensive work in the background while better using multikernel processors.

Negative user feedback to the prerelease ended up striking tab-switching and preview mode from the feature list for good. To make up for it, the Shiretoko beta supports the video and audio tags of the new HTML5, a W3C Geolocation API, JavaScript query selectors, CSS2.1 and CSS3, SVG transformations and offline applications. An extra sweet is that the new version promises 54 languages.

An initial quick test of this magazine's showed the Firefox beta to be truly faster, especially with JavaScript-heavy pages. The Acid3 test proved a bit less successful, with just a few points shy of 100. (The new Opera has meanwhile shown a perfect score.)

The Mozilla team asks users to give the beta a comprehensive look-see, while staying clear of suggesting putting the release into production. Interested parties can follow along the progress at the Firefox 3.1 Planning Center (including how to pronounce the word "Shiretoko").

The second beta of Firefox 3.1 has arrived with a new JavaScript engine, data security mode and web worker threads.