I'm using waterfox, the add-on works by stopping the htm5 video autoplay, but it doesn't stop video buffering, I can live with this limitation, but the biggest issue that made me uninstalling the add-on is the add-on somehow lags the browser when enabled. FYI I have multiple tabs opened with tabmixplus add-on. Also, the toolbar button UI is a bit buggy (maybe it's waterfox compatibility issue)