Mozilla Firefox is an open source web browser. XULRunner provides the XUL Runtime environment for Mozilla Firefox. An invalid free flaw was found in Firefox"s plugin handler. Malicious web content could result in an invalid memory pointer being freed, causing Firefox to crash or, potentially, execute arbitrary code with the privileges of the user running the Firefox application. All Firefox users should upgrade to these updated packages, which contain a backported patch that corrects this issue. After installing the update, Firefox must be restarted for the changes to take effect.