Rated 5 out of 5 stars
To the developer: This extension has been broken in the last two UX Nightlies because the URL bar and the back/forward button have been combined into one taskbar element (https://bugzilla.mozilla.org/show_bug.cgi?id=755598). It sounds like it'll also break on the downstream channels whenever the new Australis theme lands.
I guess the fix would be to create a standalone URL bar.
Anyways, thanks for your work on this!