It looks like that can only be triggered if the user interacts with the extension in some way. Presumably, then, it won't work if there's a script that should run on each page load.

EDIT: I had a look at the manifest.json[1], and it turns out that's the only permission I've requested. Not sure why Firefox says I'm asking for everything and the kitchen sink.

[1] https://github.com/Rumperuu/Pinpointer/blob/master/manifest....