For a general example, here's an example php file to be called ".php":
$value = $_POST["extension"];
header("Location: http://scirra." . $value);
In my event editor:
Button Clicked => AJAX: Post "extension=com" to .php file
=>Browser: Change URL to .php file
How do I make it so that when I click the button, the extension "com" gets POSTed to the php page, and then have the button successfully bring me to scirra.com?