So, I have read that it is possible to trace the IP of a Facebook friend while talking to him on chat by using Fiddler and Firebug. Now, as far as I am know, Facebook uses HTTPS and all in all, I cannot seem to get anything precise from Fiddler.
May anyone be kind enough to explain if this is really possible and if so, how the process goes?
I dont have a direct answer to your question, but i can give you some guidelines:
If the chat is working as a peer-to-peer network (which i highly doubt) you can trace the incoming tcp/udp connection and search it for the message using a sniffing program (like wireshark) and from there fetch their IP.
If the chat is based on that every message goes through a server (which is probably based on SOMM. not that it matters. (Server Oriented Messaging Model)). now if it is that way there is virtually no way to figure out the IP because the servers are acting as a proxy and masking the original IP, however. if FB includes some sort of meta data (which they do for location for phones etc.) that might contain the sender IP and some other stuff like the mac address etc etc. now i'm not sure of that but its a good place to look.
If you want help with firebug and all those other html/http/browser development tools there are plenty of tutorials out there. If you already know how to use it you might want to check the resources that's loaded when a message is sent. From experience i can tell that when a comment is added to something a whole bunch of crap happens that append stuff to the current html document. but i have never ever seen some meta data through that. anyway it's a good place to start.