In Firefox, you can disable media.autoplay.enabled (false) for html5 video. Flash should be disabled by default I think but you can make it dependent to click-to-play.<p>I agree with everybody, it&#x27;s such a lack a respect for the user. People using that trick (like youtube gesman pointed out) don&#x27;t think of you as individual but as receiver&#x2F;consumer&#x2F;goods&#x2F;idiot. If it uses sound, it can even be dangerous if you are using headphones.