Firebug internals & debug PHP with firePHP

Firebug internals - MDC - 這篇介紹了 Firebug 的構造組成 & how to extend firebug
FirePHP - Extending Firebug < Reference
FirePHP - Firebug Extension for AJAX Development

FirePHP adds a "Server" tab to each request in the Firebug Net and Console panels displaying data from the FirePHP-Data response header.