Origin is null in Greasemonkey https://github.com/greasemonkey/greasemonkey/issues/3111

origin-test.user.js

// ==UserScript==
// @name         httpbin.org/post XMLHttpRequest Origin header test
// @description  Origin is null in Greasemonkey https://github.com/greasemonkey/greasemonkey/issues/3111
// @version      1
// @author       jesus2099
// @grant        none
// @match        *://httpbin.org/*
// ==/UserScript==
var xhr = new XMLHttpRequest();
xhr.addEventListener("load", function(event) {
	alert(this.responseText);
});
xhr.open("POST", location.protocol + "//" + location.host + "/post", true);
xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
setTimeout(function() { xhr.send("toto=1&tutu=bob"); }, 1000);