A quick way to sanitise GET, POST, and REQUEST parameters while Facebook fixes the "slash bug": https://developers.facebook.com/bugs/567466826646137?browse=external_tasks_search_results_521473ef5f0e92913307282

sanitise-slash-bug.php

/**
 * Temporary GLOBAL Facebook fix for appended slash.
 * - Keep in mind that this can have side-effects if you have any data where you ACTUALLY use / at the end.
 * - Place this at the beginning of your code, preferably in a file that all of your apps include.
 **/
	foreach($_REQUEST as $key=>$val) $_REQUEST[$key] = rtrim($val, '/');
	foreach($_GET as $key=>$val) $_GET[$key] = rtrim($val, '/');
	foreach($_POST as $key=>$val) $_POST[$key] = rtrim($val, '/');
	
/**
 * Temporary specific Facebook fix for appended slash.
 * - This is much safer than the above, but may require modification in several places.
 **/
 	$_GET['a_specific_key'] = rtrim($_GET['a_specific_key'], '/');