It doesn't work Rated 1 out of 5 stars
I'm running FF 7.0.1 on a Mac (I was running 3.6.23 until a week ago, and it didn't work on that one, either - even the link for the older version didn't work) along with AdBlock Plus, Privacy Suite and various other security addons...plus I block various cookies if they don't need to be on my system (although, I looked and I don't see one for this addon, so it's not blocked).
There is no Dislike button anywhere on my FB page. Now, It's possible that it would work if I disabled my AdBlock Plus, Privacy Suite, allowed all the FB ads and disabled some of my other addons, but I'm not going to do that. I'm not an idiot.
So, I suspect this addon is ad supported (I could be wrong, but it's totally not working), which isn't a bug. It's just not disclosed. The dev needs to get in here, or on his FB page, and respond to complaints. Ta. Off to remove this useless thing. "Something is rotten in the state of Denmark." William Shakespeare (Hamlet; Act 1, Scene 4, Marcellus speaking to Hamlet)