How do I make a Firefox extension (add-on) that only becomes available for a specific site?

Question

I want to develop an extension that activates only for a specific domain.
I don't want it to appear in browser menus while not browsing this specific domain.

Is it possible to do that?

Answer 1

Possible: for the menus you could add a popupshowing listener that checks the currently loaded URL (docs for the context menu, where this would make the most sense).

You can also update always visible elements (like status bar icons) whenever the currently displayed URL is changed. This is done via gBrowser.addEventListener.