Empty userscript using jQuery compatible with both Firefox (Greasemonkey) and Google Chrome (with Tampermonkey)

gistfile1.js

// ==UserScript==
// @name        My Script
// @namespace   com.example
// @description Script description
// @include     https://*.example.com/url/*
// @version     0.1
// @require  https://ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js
// @grant    GM_info
// ==/UserScript==

var debug = false;

var start = function (jQuery) {
  // do your stuff
};

/*
http://stackoverflow.com/questions/2246901/how-can-i-use-jquery-in-greasemonkey-scripts-in-google-chrome/12751531#12751531
 */

if (typeof jQuery === "function") {
    if (debug){
        console.log ("Running with local copy of jQuery!");
    }
    start(jQuery);
}
else {
    if (debug){
        console.log ("Fetching jQuery from some 3rd-party server.");
    }
    add_jQuery (start, "1");
}

function add_jQuery (callbackFn, jqVersion) {
    var jqVersion   = jqVersion || "1";
    var D           = document;
    var targ        = D.getElementsByTagName ('head')[0] || D.body || D.documentElement;
    var scriptNode  = D.createElement ('script');
    scriptNode.src  = 'https://ajax.googleapis.com/ajax/libs/jquery/'
                    + jqVersion
                    + '/jquery.min.js'
                    ;
    scriptNode.addEventListener ("load", function () {
        var scriptNode          = D.createElement ("script");
        scriptNode.textContent  =
            'var gm_jQuery  = jQuery.noConflict (true);\n'
            + '(' + callbackFn.toString () + ')(gm_jQuery);'
        ;
        targ.appendChild (scriptNode);
    }, false);
    targ.appendChild (scriptNode);
}