Development of any browser plug-ins has nothing to do with ASP.NET. I think you have no clue of what you want to achieve and/or unaware of the purpose of ASP.NET; don't know how about your client, maybe you misunderstood the requirements. To learn what ASP.NET does, please see:
http://en.wikipedia.org/wiki/ASP.NET[
^],
http://www.asp.net/get-started[
^].
After we revealed that the question makes no sense, I think discussion of the plug-in development also makes no sense, as it might be just a waste of time.
—SA