So today I learned that if you have firebug installed on your Firefox, you can basically kiss web-surfing goodbye. But while you are taking a peek beneath the surface, you can run into some pretty cool apps, and this is no exception. According to http://www.charlesproxy.com :

Charles is an HTTP proxy / monitor / Reverse Proxy that enables a developer to view all of the HTTP and SSL traffic between their machine and the Internet, including requests, responses and HTTP headers.

This comes in mighty handy when you are passing variables to various analytics and metrics system, while not having the original source code in front of you.

In one day it has proven its weight in gold to me.

*Notable second runner up is Firefox plugin OmniBug.