Mozilla developers have released an updated version of their Firefox browser that fixes a number of security issues, four of them rated critical.

The update was released last week, and Firefox users should receive the patches via the browser's automatic update system over the next few days, according to Mozilla.

Research firm Secunia rates the flaws as 'highly critical', saying they can be exploited "to conduct man-in-the-middle, spoofing and cross-site scripting attacks, and potentially compromise a user's system", according to an alert. Secunia's alert can be found here.

Web surfers who want to download the Firefox update directly can find it here.

In addition to the four critical patches, the software also fixes three less critical issues and offers some stability enhancements according to the Mozilla website. Details on the security vulnerabilities can be found here.

Browser hackers have traditionally focused on Microsoft's Internet Explorer, but as Firefox's market share has grown it has become a more attractive target. Firefox is now used by about 13 percent of web surfers, according to research firm OneStat.

It has been a busy week for IT administrators looking to stay on top of security. Important security patches were also released by Microsoft and Apple.

On Tuesday last week, Microsoft released its monthly set of security patches, fixing a critical bug in its Publisher product. The company also re-released two of its August patches to fix bugs in the updates. More information on Microsoft's patches can be found here.

That was followed last Wednesday by Apple's fix for its QuickTime multimedia software. This update, rated as highly critical by Secunia, fixes six bugs in the product. More details on the QuickTime update can be found on Apple's website.