firefox mobile triple tap for fullscreen

fenix_fullscreen_triple_tap.user.js

// ==UserScript==
// @name         triple touch to fullscreen
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  triple touch to fullscreen for for mobile
// @author       trapier
// @run-at       document-end
// @match        http(s)?://*/*
// @include      http://*
// @include      https://*
// @icon         https://www.google.com/s2/favicons?sz=64&domain=tampermonkey.net
// @grant        none
// @license      MIT
// ==/UserScript==

// copy-pasted from https://greasyfork.org/en/scripts/439695-long-touch-to-fullscreen
// notch support (viewport-fit=cover) from
// - https://github.com/mozilla-mobile/fenix/issues/4149#issuecomment-610432974
// - https://stackoverflow.com/questions/2568760/is-it-possible-to-use-javascript-to-change-the-meta-tags-of-the-page/66057831#66057831

(function() {
    'use strict';
    let time_list = []
    function fullscreen() {
        // console.log('touch end')
        time_list = [...time_list.slice(-2) , +new Date()]
        const [a, b, c] = time_list
        if (a && c && c - a < 1500) {
            let metaViewport = document.head.children.viewport
            if (metaViewport == null) {
                metaViewport = document.createElement('meta')
                metaViewport.name = 'viewport'
                document.head.append(metaViewport)
            }
            metaViewport.content = 'width=device-width, initial-scale=1.0, viewport-fit=cover'
            document.documentElement.requestFullscreen()
        }
    }

    document.body.addEventListener('touchend', fullscreen )
    document.body.addEventListener('click', fullscreen )

})();