I only have autoplay issues with one site. (Yahoo Finance) Firefox can block autoplay on initial load, but not when changing back and forth between tabs nor when scrolling up and down the page. After installing this add-on, it seems to help block autoplay when switching between tabs, but allowed autoplay when scrolling up and down the page. I believe Yahoo uses multiple triggers to force the videos to autoplay .. onHover, onFocus, etc. If it is updated to catch the other triggers, I will try it again.