Hello, World.user.js

(function() {

// ==UserScript==
// @name          Hello, World
// @namespace     http://localhost
// @description   JavaScript alert box saying Hello, world
// @copyright     2007+, Marti Martz (http://userscripts.org/users/37004)
// @license       GPL version 3 or any later version; http://www.gnu.org/copyleft/gpl.html
// @license       (CC); http://creativecommons.org/licenses/by-nc-sa/3.0/
// @version       0.0.1
// @include       http://www.example.com/*
// @include       http://www.example.net/*
// @include       http://www.example.org/*
// ==/UserScript==

  alert('Hello, World!');

})();