well, I correct the code and now i can login under IE and firefox...
in login.php
(near line 74) FIND
setcookie($cookie_name, serialize(array($db_username, $form_password_hash)), $expire, $cookie_path, $cookie_domain, $cookie_secure);REPLACE BY
if(!setcookie($cookie_name, serialize(array($db_username, $form_password_hash)), $expire, $cookie_path, $cookie_domain, $cookie_secure))
setcookie($cookie_name, serialize(array($db_username, $form_password_hash)), 600);thanks a lot for your help 
