Firefox setResponseHeader isn't working - http-headers

Question

I'm working on a web application where I need to access elements of an iFrame using JavaScript. To do that, the iFrame has to send an "Allow-Control-Allow-Origin: *" header to the browser.
Unfortunately this doesn't happen, that's why I'm using an extension to modify the response headers, but for some reason, setResponseHeader doesn't work.
It gets even more confusing since I'm using setResponseHeader to strip X-Frame-Options, but when I'm setting a custom header, it just won't work.
I'm using Firefox's "Inspect Element"'s Network tab to observe the requests, and while it shows the request header being set correctly, it doesn't show the response header.
That's how I'm setting the request and response headers.
var chrome = require("chrome");
chrome.Cc["#mozilla.org/observer-service;1"].getService( chrome.Ci.nsIObserverService ).addObserver({
observe : function(subject, topic, data) {
var channel = subject.QueryInterface( chrome.Ci.nsIHttpChannel );
channel.setRequestHeader("x-mysite-extended", "somedata", false);
}
},"http-on-modify-request",false);
chrome.Cc["#mozilla.org/observer-service;1"].getService( chrome.Ci.nsIObserverService ).addObserver({
observe : function(subject, topic, data) {
var channel = subject.QueryInterface( chrome.Ci.nsIHttpChannel );
channel.setResponseHeader("x-mysite-extended", "somedata", false);
}
},"http-on-examine-response",false);
Again, the request header works according to the Network tab. I tried http-on-modify-request to set the response header but that didn't work as well.
That's how I'm stripping of the X-Frame-Options header, which works.
let myListener =
{
observe : function (aSubject, aTopic, aData)
{
console.log(aTopic);
if (aTopic == "http-on-examine-response")
{
let channel = aSubject.QueryInterface(Ci.nsIHttpChannel);
try
{ // getResponseHeader will throw if the header isn't set
let hasXFO = channel.getResponseHeader('X-Frame-Options');
if (hasXFO)
{
// Header found, disable it
channel.setResponseHeader('X-Frame-Options', '', false);
}
}
catch (e) {}
}
}
}
var observerService = Cc["#mozilla.org/observer-service;1"]
.getService(Ci.nsIObserverService);
observerService.addObserver(myListener, "http-on-examine-response", false);
I've been trying to solve this for two hours now so any help is appreciated. Thanks.

Answer 1

You're adding obserer for http-on-examine-response, with this you can only getResponseHeader
change it to http-on-modify-request. then you can setRequestHeader, you cant getResponseHeader in on modify request though.
This is scrap code but it worked for me:
observe : function(aSubject, aTopic, aData) {
// Make sure it is our connection first.
if (aSubject == channel) {
//this is our channel
//alert('is my mine');
cdxFire.myChannel = aSubject.QueryInterface(Components.interfaces.nsIHttpChannel);
if (cdxFire.myChannel.requestMethod == 'GET') {
//alert('its a get so need to removeObserver now');
//cdxFire.observerService.removeObserver(modHeaderListener, "http-on-modify-request");
}
if (aTopic == 'http-on-modify-request' && cdxFire.myChannel.requestMethod == 'POST') {
//can set headers here including cookie
try {
var xContentLength = httpChannel.getRequestHeader('Content-Length');
var xContentType = httpChannel.getRequestHeader('Content-Type');
//alert('content length is there so change it up');
cdxFire.myChannel.setRequestHeader('Content-Type','',false);
cdxFire.myChannel.setRequestHeader('Content-Type',xContentType,false);
cdxFire.myChannel.setRequestHeader('Content-Length','',false);
cdxFire.myChannel.setRequestHeader('Content-Length',xContentLength,false);