Mozilla is disabling a pair of components stealthily installed by Microsoft earlier this year for Windows users of the Firefox Web browser, warning that the plug-in suffers from a serious security vulnerability. Firefox users may already have seen a pop-up notice about an unstable or insecure add-on being disabled. The message would look something like image below. There's a short backstory to this drama. In May, I wrote about a Windows patch for the Microsoft .NET package that silently installed the Microsoft .NET Framework Assistant add-on into Firefox. The package also included an associated plug-in for Firefox called the Windows Presentation Foundation plug-in. The Mozilla user community was up arms over not just the fact that Microsoft was introducing unwanted components that could potentially weaken the security of Firefox, but that Redmond had made the thing almost impossible to remove. Microsoft's initial response -- that the add-on could be removed