F6 alt+Enter does the same thing Rated 2 out of 5 stars

If the URL in the address bar is highlighted (shortcut for that is F6), pressing Alt+Enter will duplicate it. There's no need for that part of this add-on, it's built in. I haven't used the other features, but they sound useful.

This review is for a previous version of the add-on (1.0.1).