i have a problem with a http post call in firefox. I know that when there are a cross origin, firefox first do a OPTIONS before the POST to know the access-control-allow headers. With this code i dont have any problem: Net.requestSpeech.prototype.post = function(url, data) { if(this.xhr != null) { this.xhr.open("POST", url); this.xhr.onreadystatechange = Net.requestSpeech.eventFunction; this.xhr.setRequestHeader("Content-Type", "application/json; charset=utf-8"); this.xhr.send(data); } } I test this code with a simple html that invokes this function. Everything is ok and i have the response of the OPTIONS and POST, and i process the response. But, i'm trying to integrate this code with an existen application with uses jquery (i dont know if this is a problem), when the send(data) executes in this case, the browser (firefox) do the same, first do a OPTION request, but in this case dont receive the response of the server and puts this message in console: [18:48:13.529] OPTIONS http://localhost:8111/ [undefined 31ms] Undefined... the undefined is because dont receive the response, but the code is the same, i dont know why in this case the option dont receive the response, someone have an idea? i debug my server app and the OPTIONS arrive ok to the server, but it seems like the browser dont wait to the response. edit more later: ok i think that the problem is when i run with a simple html with a SCRIPT tag that invokes the method who do the request run ok, but in this app that dont receive the response, i have a form that do a onsubmit event, i think that the submit event returns very fast and the browser dont have time to get the OPTIONS request. edit more later later: WTF, i resolve the problem make the POST request to sync: this.xhr.open("POST", url, false); The submit reponse very quickly and can't wait to the OPTION response of the browser, any idea to this?