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 late Thursday, and Firefox users should receive the 18.104.22.168 patches via the browser\u2019s 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\u2019s system," according to an alert. Secunia\u2019s 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\u2019s Internet Explorer, but as Firefox\u2019s 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.com.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 Computer.On Tuesday, Microsoft released its monthly set of security patches, fixing a critical bug in its Publisher product. The company also rereleased two of its August patches to fix bugs in the updates. More information on Microsoft\u2019s patches can be found here.That was followed Wednesday by Apple\u2019s 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\u2019s website.By Robert McMillan, IDG News Service (San Francisco Bureau)Keep checking in at our Security Feed for updated news coverage.