In your extension, you're using ABSPATH like so:
require_once(ABSPATH . "wp-content/plugins/facebook-like-button/inc/local.inc.php");
it would be better for people who do not have their wp-content under ABSPATH to use
require_once(dirname(__FILE__) . "/inc/local.inc.php");
and likewise for all other files that are being required. Please change that so I don't have to for every update you release.