As a number of people have reported, a recent update to Microsoft’s .NET Framework resulted in an add-on being installed into Firefox. Shortly after this patch was released through Windows Update, we were in contact with Microsoft to see how to resolve this issue, as we were hearing directly and indirectly from users that they wanted to uninstall the add-on, and were unable to do so through the Firefox Add-on Manager.
Until recently, removing this add-on from Firefox required that users manually edit the registry, but I’m pleased to report that Microsoft has made available a downloadable patch, and has now added it to the knowledge base article on the topic. Once this patch is applied, the add-on can be uninstalled per-user. (On Windows 7 Release Candidate, the add-on is already the fixed version, at least in my own testing.)
The add-on that was delivered through Windows Update is not compatible with Firefox 3.5, so we’re still trying to figure out how to make sure that 250M-or-so users aren’t confused or — worse — scared off of the upgrade when they are informed that this add-on will be disabled. I’ll report back when we know how that’s going to work, hopefully before Firefox 3.5 is released!
[Edit: removed reference to "disabling".]