It works fine, even if I prefer to use the equivalent script for Tampermonkey now. It's just a preference, because both solutions give the same results. For those who also use the script "Local Youtube Downloader", the dislike number won't show in both cases (add-on and script). So I guess there's an issue from the downloader script that prevents the dislike number to be displayed. When I switch it off, the number is displayed again.