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Approximately a year after pushing out the third generation of its Firefox browser, Mozilla released its first major update on Tuesday, version 3.5. Initially scheduled in March as Firefox 3.1, the release was delayed and renamed to account for a bevy of new features Mozilla had in the works.

This most important update includes a major refresh to the Tracemonkey JavaScript engine to make the browser play well with JavaScript. Firefox has a long, sordid history of buggy JavaScript interactions. Since the release of Firefox 3, Mozilla has had to put out numerous minor updates to patch up JavaScript related security flaws. Most recent was an update this month that had to address a critical vulnerability that allowed scripts from page content to run with elevated privileges.

Also included in this latest update is a new Private Browsing mode. Users engaged in Private Browsing are assured by Mozilla that nothing encountered on the Web will be stored during the browsing session. There’s also a special feature called Forget this Site that removes any trace of that site from your browser, plus a new ability to clear only recent browsing history. Other feature additions include location aware browsing, and support for open video and audio. Mozilla also tweaked performance aspects of Firefox. According to the company, this latest release is twice as fast as Firefox 3 and ten times faster than Firefox 2.