Very good and usefull addon, thanks for it.
But it miss one thing, when you close one of the active tab you switched between, it stops and wait when you activate second tab again with a mouse, then it starts to switch again.

In Chrome, quite the same addon worked better, when you close one of the tab, it starts to switched between previous active tab, then next and next, it goes down by active tabs history, very handy and saves a lot of time.