Rated 2 out of 5 stars

It's pretty sad that Microsoft still makes junk like this (just like the Bing Bar). I mean this maybe useful for people who use ClickOnce or I just think its plain wrong for you guys to just install without any permission to the user. If people want to use ClickOnce then they will download it themselves. This gets installed when you use .net framework (i think).
Anyways, for the people who strongly dislike this, you can uninstall it, using the directions provided by Microsoft (note, use Method 2):

Hi NightDrift,
I'd just like to clarify a few things. First off, the issue you're describing was true in .NET 3.5 SP1, shipped years ago, and was fixed via a patch and on Windows Update after it became known. It has not been true for any version of the extension that supported FireFox 3.0 or later (1.1+ I believe, this is 1.3.1). This extension is the work of a single person at Microsoft, who dearly loves both ClickOnce and WPF Browser Applications (partial-trust ClickOnce apps). No version of .NET includes this extension. Nothing stops you from uninstalling it. There are many customers who use .applications, and out of care for these customers we continue to keep supporting new versions of FireFox. While I understand it may be fun or easy to poke fun at Microsoft, it's not valid to say that this is spyware, forcibly put on people's machines, useless, etcetera.