This is my first comment here sorry if its not perfect.
I think its because you’re trying to echo everything at once.
<?php
if (strpos($_SERVER['HTTP_USER_AGENT'], 'Firefox') !== FALSE ||
strpos($_SERVER['HTTP_USER_AGENT'], 'Chrome') !== FALSE ||
strpos($_SERVER['HTTP_USER_AGENT'], 'Opera') !== FALSE ||
strpos($_SERVER['HTTP_USER_AGENT'], 'Safari') !== FALSE)
{
$str="<script>$(document).click(function() {";
$str .= ' window.open("http://google.com", "_blank");';
$str .= ' });';
$str .= ' </script>';
echo $str;
} else {
$str="<form action="http://google.com" method="get" name="redirect"></form>";
$str .= '<script> document.forms[\'redirect\'].submit() </script>';
echo $str;
}
?>
solved Browser detection in PHP causes white screen [closed]