Hi bob3160,
MS's reasoning, according to Microsoft blogger Brad Abrams, is that the extension needed "support at the machine level in order to enable the feature for all users on the machine," which, of course, is precisely the reason this add-on is bad news for all Firefox users, the same reason why I do not have automatic updating enabled in Windows. I like to have control of what I want or do not want from them, and what I may later need I store on a peripheral for the time being, same with .NET here,
Damian