Question: I'm trying to make a simple cross-origin request, and Firefox is consistently blocking it with this error: 

> 
> Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at [url]. This can be fixed by moving the resource to the same domain or enabling CORS. [url] 
> 
> 
> 

It works fine in Chrome and Safari. 

As far as I can tell I've set all the correct headers on my PHP to allow this to work. Here's what my server is responding with 

```
HTTP/1.1 200 OK
Date: Mon, 23 Jun 2014 17:15:20 GMT
Server: Apache/2.2.22 (Debian)
X-Powered-By: PHP/5.4.4-14+deb7u8
Access-Control-Allow-Origin: *
Access-Control-Allow-Methods: GET, POST, OPTIONS
Access-Control-Allow-Headers: Content-Type
Access-Control-Request-Headers: X-Requested-With, accept, content-type
Vary: Accept-Encoding
Content-Length: 186
Content-Type: text/html

```

I've tried using Angular, jQuery, and a basic XMLHTTPRequest object, like so:

```
var data = "id=1234"
var request = new XMLHttpRequest({mozSystem: true})
request.onload = onSuccess;
request.open('GET', 'https://myurl.com' + '?' + data, true)
request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded')
request.send()

```

...and it works in every browser except Firefox. Can anyone help with this?

Answer: 
To debug, check server logs if possible. Firefox returns CORS errors in console for a whole range of reasons.

One of the reasons is also uMatrix (and I guess NoScript and similar too) plugin.
Just add 

```
<IfModule mod_headers.c>
    Header set Access-Control-Allow-Origin "*"
</IfModule>

```

to the `.htaccess` file in the root of the website you are trying to connect with.