I was having trouble testing some hreview elements today and assumed I had the latest version of Tails. Fortunately, a link on Microformatique suggested visiting the Tails home page to really get the most recent version.
If you have this extension in Firefox, do not count on the usual ff extension update thingamabob to work. Go to the Tails site today and get the latest version (.3.7). It is much, much better than the one I used to have (.3.1).