Checking that with DEBUG mode shows you are using the variable $url before it has been declared and initialized. It gives this notice:
Notice: Undefined variable: in the file /wp-content/plugins/wpmu-dev-facebook/lib/class_wdfb_admin_form_renderer.php.
While checking the code, I saw that you are using the $url variable in line 223, when defining and initializing it only in line 226.
Notice: Undefined variable: in the file
The $width variable is defined inside the scope of an 'if' statement (line 79) and used outside that 'if' statement (line 86).
Can you please check that?