Don't blame the developer Rated 5 out of 5 stars
The button is absent on the recently updated Youtube design. It is the new design of their webpage that is the problem and not this add-on's fault. You will notice that other mp3 downloaded add-ons are also suffering the same problems. I'm sure that there is a real possibility that there will be a subsequent update for this add-on to take into account the Youtube design change.
Prior to the recent alteration, this add-on worked perfectly and seamlessly. Perhaps if people did a little detective work they wouldn't make such rash assumptions and always blame the add-on.