I like the very simple API to FirePHP and find it very useful for debugging Wordpress plugins and themes. There are a few other plugins out there that integrate FirePHP, notably [WP-FirePHP] (
http://wordpress.org/extend/plugins/wp-firephp/) and [Wordpress Logger] (
http://wordpress.org/extend/plugins/wordpress-logger/), but both add complexity that I don't want to have to deal with for a quick debugging task.
It wouldn't be that hard to install the FirePHP core and add the includes to wp-config.php, and that's what I generally do on sites that I control, but having this plugin in the
Wrodpress.org/extend directory means that I'll be able to install it on the fly for a blog that someone hasn't given me shell or ftp access to.