Apparently the extensions aren't reliable at all. I saw a video at one point where a guy went over why you cannot trust the extensions and how the numbers are pure fiction, but I forget the exact reasons. I think one example was that the same video would have vastly differnet numbers of down votes depending on the person with the extension. Something something confirmation bias.

For me, it doesn't really matter. I still down vote when I dislike a video. They may not count my vote at all, but I still do it out of stubbornness.