I am trying to do "POST" with XMLHttpRequest in a firefox extension, and after that I try to get the "Location" header and open it in a new tab. For some reason, the XMLHttpRequest doesn't contain a location header.

My code

function web(url,request)
{
    var http = new XMLHttpRequest();
    http.open('POST',url,true);
    http.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
    http.onreadystatechange=function() {
    if(http.readyState == 2) {
        alert(http.getResponseHeader("Location"));
        }
    }
    http.send(request);
}

Also, if I change the alert to getAllResponseHeaders() to see all headers, I just don't see the location header there. If I try to spy on the request of the original site with Firebug, it does show me the location header in the response. Please help me resolve my issues. Thanks :)

P.S. I'm also unable to open a link in new tab using window.open(url, this.window.title);, but as that's not directly related to the rest of this I'll post a separate question to ask about it.