The Mozilla Foundation released on Tuesday an updated version of its popular, free Web browser, Firefox, which features improved search functions and more protection against spyware.

Firefox is the product of hundreds of volunteer software developers around the world, who collaborate to design new features and fix bugs — unlike proprietary browsers such as Microsoft Corp.'s (MSFT ) Internet Explorer, whose source code is kept secret.

The Mountain View-based Mozilla Foundation bills itself as a nonprofit "dedicated to improving the Internet experience for people everywhere."

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Firefox 1.0 was released officially in November 2004, and it quickly became one of the most downloaded open-source programs in the world. It's particularly popular among home PC users and college students.

Within 99 days of its release, the program was downloaded more than 25 million times. By August, it had been downloaded 200 million times.

Mozilla officials estimate that more than 70 million individuals are using Firefox, which has been translated into 35 languages and is available for the Windows, Mac or Linux operating systems.

Improvements to Firefox 2.0 make it tougher for spammers and other advertisers to put "spyware" and other invasive programs on users' computers.

Some changes, such as an integrated spell check, are meant to help Internet users who post text on blogs, community sites such as MySpace.com or YouTube, or on collaborative Web sites known as "wikis."

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