Where can i find the code that sends POSTs and/or GETs to mozilla

Hello all,

Despite of quite a lot of searching, I was not able to find the place
where POSTs and GETs are handled: I.e. an user enters something into a
form inside the browser, and clicks submit, which code is launched?

Concretely i am interested in the method how do you send the GET/POST
request to mozilla and how do you get back the response etc.

TIA,
Peter
---
http://www.rubyrailways.com