I don't understand Rated 2 out of 5 stars

I don't understand what this does and why it seems to be desperately needed on my system, it updates every time I run Firefox so, any clarification would be appreciated, especially as to why it updates to version 0.0.0

Update .NET 3.5

Hi Kenpei,
The 0.0.0 version shipped as part of the per-user update (see here: http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=9923 ) but I'm unsure why it's happening every time you start FF. This is not the same as this copy of the extension, which is only the same in name to the original.

If you do not run ClickOnce .applications on your machine, I suggest just following the instructions you can find on the web (or on the reviews for THIS extension) to remove it... example: http://support.microsoft.com/kb/963707 .