Rated 1 out of 5 stars
Does not work on 20.0.1. Sad that the FF developers put their own desires above the users when removing the long-standing ESC key functionality. Sadder that they then cited the existence of this add-on to justify their refusal to restore the traditional ESC key functionality, and this add-on doesn't even work.
2013-04-17 ETA - I filed an issue as requested: https://github.com/gavinsharp/SuperStop/issues/2
Sorry you're having trouble! The add-on is working for me in Firefox 20.0.1 on Mac. Could you file an "issue" at https://github.com/gavinsharp/SuperStop/issues so that I could look into your problem further?