FireConsole is the next incarnation of the popular FirePHP Firefox Extension. It is a complete re-write for Firefox 3.5+ and Firebug 1.5+ on top of a new narwhalrunner -> narwhal-xulrunner -> narwhal -> CommonJS stack. This means it is easily extensible!
FireConsole is currently under development. You can follow progress of the alpha on twitter.
You can watch a HD version on vimeo.