You would think Microsoft would have learned its lesson after all the negative backlash with the Microsoft .NET Spyware Extension. But this is Microsoft we are talking about. Earlier today I got an odd pop-up window from Firefox: The Windows Presentation Foundation plug-in has been disabled for your protection. Several people on Go Firefox! have reported getting the same message. From what I have read this plug-in that allows the embedding of XAML applications (an XML-based UI technology) in web pages, called XBAP and is part of the .NET Framework 3.5 SP1. On Tuesday, Microsoft announced a security hole was…