GM_Issue_1081.user.js

// ==UserScript==
// @name           Issue 1081
// @namespace      gm
// @include        *
// ==/UserScript==

var xhr = GM_xmlhttpRequest({
	method: "GET",
	url: "http://www.github.com"
});

try{
	xhr.upload.addEventListener("progress", function(){
		console.log(this, arguments);
	}, false);
}catch(e){
	console.log(e);
}

try{
	console.log(xhr.upload.onprogress);
}catch(e){
	console.log(e);
}