How to build Firefox extention to intercept HTTP requests and responses?

Question

how do I insert a listener to Firefox http requests and responses, so that I popup a window with the address requested and the response body?

Note:

I have to do this building an extension to Firefox.
I need a button to activate or disable the feature.
For every request, I need to popup a window with an "Ok" button to allow the request to be made. Likewise, I need to popup a window with the response body from the web server, with an "Ok" button to allow the content to be displayed by the browser.

I know that I have to use nsIHttpChannel, as shown here, but I don't know where to put such code on the extention's architecture.
I have very little knowledge about javascript.

Could anyone help me?

Answer 1

It might help to take a look at Firebug source code

http://code.google.com/p/fbug/