Mozilla Unveils First Firefox 3.6 Beta

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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 June 2009's Firefox 3.5 . 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 "Personas" 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, Mozilla debuted plug-in checking 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 manually check 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 "Some plug-ins used by this page are out of date," the message reads.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 Mozilla developer center blog , and start-up times have been reduced.

Some features once destined for Firefox 3.6, however, have been dropped, including one that was to take advantage of Microsoft's new Windows 7 . Integration with Windows 7's Jump Lists -- a feature that would list recently-visited sites when Firefox's icon is right-clicked in the taskbar -- has been postponed and wasn't included with the beta.

Support for Windows 7's Aero Peek and taskbar thumbnail previews did make it into Firefox 3.6 Beta, even though Mozilla had some last-minute work nailing down the former.

All versions of the browser now offer thumbnail previews when users cycle through the open tabs with the Ctrl-Tab key combination. The feature is disabled by default in the beta, however. To switch it on, users must edit Firefox's configuration file by entering "about:config" in the address bar, locating the "browser.ctrlTab.previews" item and double-clicking it to change its setting to "true." Firefox must be restarted for the change to take effect.