How to intercept XMLHttpRequests, including headers and responses?

[逄望舒]

I am working in a crawler project. My job is to capture asynchronous
requests and responses sent by XMLHttpRequest (XHR). I need to work
out a solution, which receives a URL and automatically intercept Ajax
requests and corresponding responses. This feature is particular
necessary in video hosting website, for considerable information, such
as Comments List and Play Count, are transferred asynchronously. I can
use either IE’s approach or Firefox (Gecko)’s approach.

I’ve tried APP Control in the control csExWB. But data is
insufficient, lacking of POST data and responses body. And in its
higher version (v2.0.0.2), two key events DownloadRequestAsynch and
DownloadRequestSynch do not work properly in my environment (Windows
XP SP3, Internet Explorer 8).

So I would like to seek for a solution through Mozilla’s approach. But
documents in the MDC seem to be out of date. Gecko Runtime Environment
(GRE) has already been substituted by XULRunner. So I’ve no idea how
to implement this feature. Anyone could help me?