Microsoft created a plugin for Firefox. It allows .NET to work seamlessly with the popular Mozilla browser. However, it also allows websites to secretly install software on your computer.
If you use Firefox and it asked you to install a .NET extension, don't do it. If you already accepted it and installed the plugin... well, you are kinda screwed. You see, Microsoft disabled the uninstall feature. Removal requires a registry hack. Just disable it, in the meantime.
via Brain Krebs at the Washington Post
:Microsoft Update Quietly Installs Firefox Extension
A routine security update for a Microsoft Windows component installed on tens of millions of computers has quietly installed an extra add-on for an untold number of users surfing the Web with Mozilla's Firefox Web browser.
Earlier this year, Microsoft shipped a bundle of updates known as a "service pack" for a programming platform called the Microsoft .NET Framework, which Microsoft and plenty of third-party developers use to run a variety of interactive programs on Windows. [...]