https://addons.mozilla.org/en-US/firefox/addon/enhancer-for-youtube/
https://addons.mozilla.org/en-US/firefox/addon/enhancer-for-youtube/
youtube.com##+js(execute-script, (function(){ const observer = new MutationObserver(() => { const v = document.querySelector('video'); if (v && v.playbackRate !== 1.5) v.playbackRate = 1.5; }); observer.observe(document.body, {childList: true, subtree: true}); })())
youtube.com##+js(set-constant, yt.config_.PLAYER_CONFIG.playbackRate, 1.5)