// start ouput buffering
ob_start();

// be sure you have uploaded the FirePHP lib on your server
require_once('lib/FirePHPCore/FirePHP.class.php');

// instantiate firephp, false would have turned logging off
$firephp = FirePHP::getInstance(true);

// See some more examples at:
// http://www.firephp.org/HQ/Use.html
$firephp->log('Message','Bob was here');

http://www.firephp.org/

This is my first encounter with FirePHP, I might be using this more often. FirePHP lets you output log lines like console.log would in FireBug. You will need the FirePhp plug-in for Firefox and you will have to upload the FirePHP lib to your server.

FirePHP example

php

PHP