Just what I've been waiting for. Rated 4 out of 5 stars

The original Last Tab was an add-on I used all the time. It broke a number of years ago, and a guy named Tim Humphrey wrote an unofficial add-on for the add-on, and it worked beautifully until Firefox got to version 20-something.
Thanks very much to Prince Samuel for coding this elegantly effective replacement that does just what it is supposed to do!