Security Update - ShellBlock ShellBlock is a security fix update for Bug 250180. It disables the ability to call the shell protocol from within affected Mozilla programs. The shell protocol allows applications to call Windows Explorer using the protocol to run the file specified on the local machine. This update is for users of Mozilla 1.x (up to Mozilla 1.7), Mozilla Firefox (up to 0.9.1), and Mozilla Thunderbird (up to 0.7.1) on Microsoft Windows 2000 and XP only. Mozilla 1.7.1, Firefox 0.9.2 and Thunderbird 0.7.2 have been released with this fix included. For more information on the issue, read What Mozilla Users should know about the shell: protocol security issue.