How to delete cookies in firefox?

Question

PHP

Simple example:
login.php file
session_start();
// log in
file logout.php
session_start();
if (isset($_COOKIE[session_name()])) {
setcookie(session_name(), '', time()-1, '/');
}
session_destroy();
In google chrome, when logout.php is launched, the phpsessid cookie is expectedly overwritten and if you go to login.php a new value appears there, in firefox the cookie value is saved.
Actually the question itself is: why is this happening and how to make the behavior of the fox be the same as that of Google Chrome?

Answer 1

$cook do delete';