how would a modify headers add-on be able to let the server think that you are coming from a different address? It's not as if the browser sends the origin address as a HTTP header.
It doesn't have to. It's part of the IP packet which contains the TCP packet which contains the request headers.
Are you sure that you are not using a proxy server at the address Wolfram gives you?
Edit: On second thought, you could try to fool server-side detection by setting a non-standard X-Forwarded-For header, but a what is my ip service shouldn't trust that and just report the real remote address.
It doesn't have to. It's part of the IP packet which contains the TCP packet which contains the request headers.
Are you sure that you are not using a proxy server at the address Wolfram gives you?
Edit: On second thought, you could try to fool server-side detection by setting a non-standard X-Forwarded-For header, but a what is my ip service shouldn't trust that and just report the real remote address.