Firefox & NPAPI plugins: can they be restricted (to be only used on certain pages)?

Question

I've been reading this and I know it doesn't mention possible ways to restrict access to an installed plugin, but is there some trick one can play in order to contain the usage of a plugin?

Answer 1

You could write your plugin to query window.location and then refuse to work if it doesn't match up with what you want =]

I don't know of another way to do it, though.