Rated 4 out of 5 stars
There is a relatively simple way to get this working on a clean install of newer versions of Firefox until the add-on is updated.
First, go here; http://www.filehippo.com/download_firefox/6825/ and download and install Firefox 3.5.7. One you do that the add-on will work, and you can then update to the newest version (currently 3.6) and the add-on will work with it.
This took me about 2 minutes and everything is working fine now. This is definitely a 5-star add-on and a must have, but since it doesn't work with clean installs of newer versions of Firefox I have to give it a 4.