Rated 5 out of 5 stars

Still my favourite gesture addon. Firefox version 21 broke some things, but don't despair, because:

VERSION 0.26 WORKS WITH FIREFOX 21

You can get it from the author's home page (look for the "Add-on home page" link on the right sidebar of this page)

This review is for a previous version of the add-on (0.25.1).  This user has a previous review of this add-on.