Mozilla has plugged two critical security holes in versions 2 and 3 of Firefox.

Version 2.0.0.16 fixes a code injection risk involving vulnerabilities in its CSS reference counter, and a flaw in handling command-line URLs that means multiple tabs can be launched when Firefox is not running. The first flaw also affects the Thunderbird email clients when JavaScript is enabled for email reading. Such a set-up is generally a bad idea.

The second flaw allows multiple tabs to be launched in Firefox even when it's not open. This is an attack vector for the Mozilla side of a blended threat ariseing when Apple's Safari browser is installed on the same systems as either Internet Explorer or Firefox. Dubbed the "carpet bombing" bug, this was disclosed by independent researcher Billy Rios in May and patched by Apple - after some foot-dragging - in June.

Mozilla has also released a stability and security upgrade for the latest version of its browser. Firefox 3.0.1 includes fixes for the same two bugs that affect the earlier version of the browser, as well as a fix for a bug specific to version 3 which means malformed GIF files pose a code injection risk to Mac OS X systems running the latest version of the browser.

Firefox 3.0.1 - the first upgrade to the latest version of Mozilla's flagship browser software - came out on Wednesday, a day after the version 2 update. Support for version 2 ends in mid-December. ®

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