Hide scrollbars completely in Firefox

hide-scrollbars.uc.js

(function () {
    const css = `
    scrollbar, scrollcorner, scrollbar thumb, scrollbar scrollbarbutton {
        pointer-events: none !important;
        -moz-appearance: none !important;
        visibility: hidden !important;
    }
    `;
    Components.utils.import("resource://gre/modules/Services.jsm");
    const sss = Components.classes["@mozilla.org/content/style-sheet-service;1"].getService(Components.interfaces.nsIStyleSheetService);
    const sheet = Services.io.newURI("data:text/css;charset=utf-8," + encodeURIComponent(css), null, null);
    sss.loadAndRegisterSheet(sheet, sss.AGENT_SHEET);
})();