youtube_tools_popout_helper.user.js

// ==UserScript==
// @name         Youtube Tools Popout Helper
// @namespace    http://tampermonkey.net/
// @version      0.2
// @description  replaces links in the end screen to point towards another embed page
// @author       necroforger
// @match        https://www.youtube.com/embed/*?*ytt_popout=1*
// @grant        none
// ==/UserScript==

(function () {
    'use strict';

    function replaceLinks() {
        let elements = document.querySelectorAll("a.ytp-suggestion-set");
        for (let x of elements) {
            if (x.getAttribute("target") !== "") {
                x.setAttribute("target", "");
            }
            if (x.getAttribute("href").includes("/watch?")) {
                let url = x.getAttribute("href");
                let id = url.substr(url.indexOf("?")).match(/(v=)(.*?)(&|$)/)[2];
                let newLocation = `https://www.youtube.com/embed/${id}?ytt_popout=1&autoplay=1`;
                x.setAttribute("href", newLocation);
            }
        }
    }

    setInterval(replaceLinks, 100);
})();