Mozilla on Monday posted Firefox 3 Beta 1, a developer preview release of the popular open source Web browser.

The latest iteration of the browser relies on the new Gecko 1.9 Web rendering engine, which is designed to enhance performance and stability, among other things. The latest version also includes a variety of improved security features, such as the ability to click on the site favicon (the graphic displayed in the URL address bar) to show site ownership information.

Firefox 3 Beta 1 also includes malware protection. But the effectiveness of using a blacklist to identify sites that distribute malware remains to be seen, given that new malware sites appear and disappear on a daily basis specifically to avoid blacklisting.

Other Firefox security features may prove more useful, like Web Page Forgery Protection, clearer SSL Error messages when invalid SSL certificates are found, automatic plug-in checking that can disable insecure plug-in updates, integration with anti-virus programs, and compliance with Microsoft Vista's Parental Control settings.

Firefox 3 Beta 1 introduces a number of ease of use enhancements. There's improved password management and add-on installation. There also a new download manager that lets you resume downloads interrupted by a crash or loss of connectivity.

"You're gonna find that it's not only fast, nimble, and featureful, but such an advance from Firefox 2 that you won't want to go back," said Mozilla's community quality advocate Asa Dotzler in a blog post on Monday.

Despite the warning that the software is being made available for testing purposes only -- to find flaws beyond the ones already known -- reviewers have been critical of Firefox 3's security.

Responding to a report last week that 80% of the bugs found in Firefox 3 would remain unrepaired by the time the software is officially released, Dotzler said in a blog post, "That claim is simply [not true]. We've already fixed over 11,000 bugs and features in Firefox 3 and now we're discussing how to handle the remaining 700 issues we wanted to get fixed for Firefox 3."

The browser's release notes offer similar assurance. "Over 300 individual memory leaks have been plugged, and a new XPCOM cycle collector completely eliminates many more," the release notes say. "Developers are continuing to work on optimizing memory use (by releasing cached objects more quickly) and reducing fragmentation."

Version 3.0 was first demonstrated at the Black Hat security show in Las Vegas, back in August.