Hides YouTube fullscreen player's scrollbar that appeared in Firefox 86
// ==UserScript==
// @name YouTube - Fix Fullscreen Scrollbar
// @namespace cprn
// @version 0.2
// @description Hides YouTube fullscreen player's scrollbar that appeared in Firefox 86
// @author cprn
// @match https://*.youtube.com/*
// @match http://*.youtube.com/*
// @grant none
// ==/UserScript==
var css = document.createElement("style");
css.innerHTML="ytd-app { --ytd-app-fullerscreen-scrollbar-width: 11px !important; }";
document.head.appendChild(css);