Firebug fantastic addon for the Firefox browser that allows you to analyze the content of the pages that you are visiting, even make modifications and see how they would be.
If you use Firebug there is an additional extension to it, called FirePHP which allows you to enter the Firebug console with PHP calls. a plugin for WordPress, WP FirePHP that allows you a total integration of both components with your Word Press.
WP FirePHP ] includes all the variables and global constants of WordPress so that you do not receive unnecessary errors and the debug process of your WordPress is as accurate as possible. It installs like any other WordPress plugin, and it's a great help. In addition, all the constants and variables are already adapted to WordPress 2.8 .