Delayed by over two weeks as developers closed out last-minute bugs, including one that pushed the release back by several days last week, Firefox 3.6 Beta contains relatively few visible changes from . Instead, most of the enhancements have been made to under-the-hood components, including the TraceMonkey JavaScript rendering engine.

Among the new features visible to users is integrated support for the scaled-down browser skins dubbed by Mozilla, and new warnings to users when they reach a site that calls on outdated plug-ins, such as Adobe's Flash Player or Apple's QuickTime.

The warning is only the last of several moves Mozilla's made in the last two months to reduce the number of users who are vulnerable to attack because they haven't updated third-party plug-ins. In early September, with updates to Firefox 3.5.3 and Firefox 3.0.14, which automatically detect outdated versions of Adobe's Flash Player and prompt users to upgrade to the newest -- and theoretically the most secure -- edition.

Since then, Mozilla has added a page on its site where users could other plug-ins for obsolete editions. Firefox 3.6 Beta, however, displays a warning when the browser is asked to call up an outdated plug-in. "Some plug-ins used by this page are out of date," the message reads.

Also debuting in the beta of Firefox 3.6, said Mike Beltzner, director of Firefox, are support for new CSS, DOM and HTML 5 technologies; support for full-screen video embedded with the video HTML tag; and support for the Web Open Font Format (WOFF). JavaScript performance has also been boosted, said Beltzner in a post to the , and start-up times have been reduced.