The architecture of FireFox extensions is quite far from .NET. Extensions do not hook up any native CPU code (not mentioning .NET managed code). They are hosted by FireFox itself; it makes them platform-independent and safe — any uncontrolled access to OS is excluded.
The developed extension is a zipped directory (zip file is renamed as *.xpi file) which contains XML-based files such as XUL and RDF, a also DTD, Java and manifest files.
Please,
Read
The
Following
Manual:
https://developer.mozilla.org/en/Building_an_Extension[
^].
—SA