Say you do not want to have a twitter account but want to look at twitter stuff. You go there and your block autoplay in firefox works when you visit the site the first time. Then you see a video you would like to play. You press the play button. You watch a video. But then... After you press play well... Autoplay is reactivated and the only thing to do is to exit firefox, do a thorough cache clean then start over again. I know you are hard at work...there! Wish this could be fixed.... Maybe mobile data providers have a backend deal to break everything to steal data and make your lives miserable. I wish this could be fixed...