This add-on was made to help the users of the PHP extension "Xdebug". It adds stylish buttons to your toolbar for toggling debugging and profiling. Toggling works by setting or erasing the XDEBUG_SESSION and XDEBUG_PROFILE cookies, just like using the PHPStorm bookmarklets. Values of these cookies can be customized from the add-on options.
The buttons have colourful and pixel perfect icons, taken from the "Farm-Fresh Web Icons" icon pack by FatCow web hosting.
If you are new to Xdebug or the cookie method, please refer to the Xdebug documentation.