Mozilla has released a new version of Firefox in response to the discovery of several security flaws in the browser software.

Version 3.0.7 of Firefox plugs five security vulnerabilities, three of which earn the dreaded "critical" label. Of these critical flaws a bug that means that Firefox crashes with evidence of memory corruption stands out as the most severe. Critical flaws in Mozilla's garbage collection process (involving memory management and "cloned XUL DOM elements") as well as bugs in the PNG library used by Mozilla also create a possible means for hackers to inject malware onto vulnerable systems.

The Firefox update also fixes a number of lesser security and stability bugs, as explained in Mozilla's release notes here. Malware exploiting the bugs is yet to be seen in circulation, but that's a poor reason to hold off upgrading. Those who have enabled Mozilla's automated update process should find that new software is installed within a day or so.

Mozilla's Thunderbird email client and SeaMonkey application suite share a similar code base to Firefox and therefore also need updating, to Thunderbird 2.0.0.21 and SeaMonkey 1.1.15, respectively.

The Firefox update was published on Thursday a day after Opera released a new version of its software, largely in response to the discovery of separate security flaws, making it a busy week on the alternative browser security front. ®