function handleRequest(request, response) { response.processAsync(); response.setHeader("Content-Type", "text/css", false); response.setHeader("Cache-Control", "no-cache", false); let timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer); timer.initWithCallback( () => { response.write("body { background: #eee; }"); response.finish(); }, 1500, Ci.nsITimer.TYPE_ONE_SHOT ); }