How to use WP-FirePHP extension?

I gave up on using the plugin and use FirePHP straight as a mu-plugin:

And firebug.php file consists of:

<?php
/*
    Plugin Name: FirePHP
    Version: 0.1
*/

require_once( 'FirePHPCore/FirePHP.class.php' );
ob_start();
$firephp = FirePHP::getInstance( true );

function logit( $var, $title="From FirePHP:" )
{
    global $firephp;
    $firephp->log( $var, $title );
}

Then I call it from anywhere (theme, plugin, core) using the function:
logit( $var_to_debug, 'The var contains:' );