It just doesn't work. I got the latest version of Firefox on Windows and I just installed this add-on and restarted the browser. Sure, I can see the one-block button on every account, tweet, like lists and retweet lists but most of the time when I click on them there is no response. It happened once that the blocking did occurred when I was on a Likes list but then I saw it was to block the OP's account instead of the one who made the like! So I had no choice but to uninstall it.