snowdenize.js

// ==UserScript==
// @name Snowdenize All Images
// @namespace net.trmm.snowdenize
// @author Trammell Hudson <hudson@trmm.net> and Cameron Cundiff <cameron@ckundo.com>
// @include *
// @Grant       none
// @version 2
// ==/UserScript==

(function() {
	var snowden = 'https://media.giphy.com/media/l0NwuLOY7KkpCERSo/giphy.gif';

	var snowdenize = function() {
		var gifs = document.querySelectorAll("img[src$='.gif']");
	
		Array.prototype.forEach.call(gifs, function(gif) {
			gif.src = snowden;
		});
	};

	snowdenize();

	var observer = new MutationObserver(function() {
		snowdenize();
	});

	observer.observe(document.body, { childList: true });

	observer.disconnect;	
})();