this question was asked many times:
- 2004
- 2005
- 2007
- 2009
- 2010
and always without answers...
Language bindings page doesn't contain C# or mono (but does so for Java and Python):
https://developer.mozilla.org/en-US/docs/Mozilla/Tech/XPCOM/Language_Bindings
There is some code - http://off.net/~shaver/mono/
But i don't see C++ part of it (and I think it is necessary as a "XPCOM Component Loader")
There is also something what is called MonoConnect
https://bugzilla.mozilla.org/show_bug.cgi?id=296672
But i didn't found it's docs in google.
I know that it is possible to implement plugin as CLR host as written here:
http://www.mono-project.com/docs/advanced/embedding/
but i don't want to reinvent the wheel,
that is why I am asking where to find an existing implementation of "Component Loader".
Here is your answer: http://lists.ximian.com/pipermail/mono-devel-list/2004-October/008215.html, first answer in your first link to a mailing list.
Here is a github link to the issue in MonoConnect. I just took some strings in the diff which is in the tracker(the link you provided) and searched in google for it, got a github repo.
As well as this: http://people.mozilla.org/~chofmann/l10n/tree/mozilla/extensions/mono/
As far as written code, this is the most you will probably get.