"This is the twelfth developer milestone focused on testing the core functionality provided by many new features and changes to the platform," Beltzner wrote in a blog. "Testers can download Firefox 3, Beta 4 builds for Windows , Mac OS X and Linux in over 35 different languages."

Security Enhancements

Improved security is a major goal. To check Web-site authenticity, users will click on the site's favicon (image) in the location bar to see the identity of the site's owner.

A Web-site indicator turns green when users access sites that employ Extended Validation SSL certificates, which add a trust component to online secure transactions by mandating that the site operators undergo vetting by an established certificate authority. Web surfers also will be able to determine whether their Internet connections are protected from eavesdropping.

Built-in malware protection warns users whenever they visit pages known to install viruses, spyware, trojans or other infections. In addition, the contents of Web pages suspected to be phishing forgeries are no longer displayed.

Firefox 3's revised download manager lets users see, and even search on, the Web site from which they have downloaded one or more files. Users also will be able to resume downloads after restarting the browser or resetting their network connections.

New Features

A new full-page zoom feature lets users scale a Web page, or they can simply change the text size. In addition, an auto-complete feature allows typing in all or part of the title, tag or address of a page to view a list of matches from the user's history and bookmarks.

Changes to Firefox 3's JavaScript engine, as well as the introduction of profile-guided optimization , provide significant performance gains, Beltzner said. "Web applications like Google Mail and Zoho office run much faster, and continued improvements to memory usage drastically reduce the amount of memory consumed over long Web-browsing sessions," he added.

Other enhancements are in the works to optimize Firefox to a user's specific requirements. For example, the beta displays icons, toolbars and other user-interface elements specific to the operating system in use, whether Vista, Linux or Mac.

Firefox 3 is closer to release than the beta Internet Explorer 8 recently previewed by Microsoft . According to the nonprofit Mozilla, a public release of Firefox 3 is planned "in early 2008."

But before that happens, Mozilla expects one more beta version will need to undergo developer scrutiny. "The development team decided that a fifth beta milestone would be required, based on the number of blockers remaining," Beltzner said.