tab context menu is better than page context menu.

@def00111, I think it would make more sense for this to be on the tab context menu instead of the page context menu, because that's where the title appears. It would also solve the problem with it not appearing when right-clicking certain parts of pages.
Ideally, you could provide an option for which menu(s) it appears in.

Sorry for putting this in a review, but I can't see any other way to contact you or contribute code.

Does what it says, seems to work well for me.

Works as expected in most cases.

If 'Copy Page Title' is missing from the contextual menu – this bugged me more than once at https://bugzilla.mozilla.org/show_bug.cgi?id=1312373 – then try clicking a different part of the page.

Firefox 53.0.3
It copies nothing