PHP Test browsers compatibility

Here a small php function for to test compatibility :

function fck_test_bronser_compatibility() {
if (ereg("(Firefox|Netscape)", $_SERVER['HTTP_USER_AGENT']) ||
(ereg("MSIE", $_SERVER['HTTP_USER_AGENT']) && ereg("Win", $_SERVER['HTTP_USER_AGENT']) && !ereg("Opera", $_SERVER['HTTP_USER_AGENT']))) {
echo "ok";
}
}

This function does't detect Mozilla ...
Mozilla seems to me difficult to be detected :
http://www.zytrax.com/tech/web/browser_ids.htm