Mozilla Monday rushed out a new version of Firefox to fix a flaw it introduced with the 12-patch security update it shipped less than a week ago.

Mozilla patches 12 Firefox bugs, a third of them critical

Firefox 3.0.10, which the open-source browser maker called a "security and stability" release, follows Firefox 3.0.9 by just six days, and was necessary because of a new bug that slipped into last week's update.

Mozilla labeled the new bug a critical security vulnerability. "One of the security fixes in Firefox 3.0.9 introduced a regression that caused some users to experience frequent crashes," the accompanying advisory said. "In analyzing this crash, we discovered that it was due to memory corruption similar to cases that have been identified as security vulnerabilities in the past."

The flaw, which cropped up only in the Windows version of Firefox, was detected by Mozilla's crash reporting system, and by last Wednesday, developers were discussing how to deal with the problem on Bugzilla, the company's bug tracking system.

"So we fixed [bug] 431260, which wasn't really a security problem, and we introduced this bug, which probably is," said Robert O'Callahan, a Mozilla developer who works on Firefox's rendering engine. "Perhaps we need to be more picky about what we land on branch."

By Thursday, a patch had been created and the new build had been passed on to testing.

This isn't the first time that Mozilla has had to deal with a regression bug, one that its own developers introduced while making other fixes. Two different times in late 2007, Mozilla released emergency updates to patch such bugs.

Firefox 3.0.10 can be downloaded for Windows, Mac OS X and Linux from the Mozilla site. Current users can also call up their browser's built-in updater or wait for the automatic update notification, which should pop up in the next 48 hours.

According to Mike Beltzner, director of Firefox, Mozilla also plans to post the delayed Firefox 3.5 Beta 4 later night.

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