Bu ekleyin.
$config->set('HTML.SafeObject', true);
$config->set('HTML.SafeEmbed', true);
Buna.
require_once '../../htmlpurifier/library/HTMLPurifier.auto.php';
$config = HTMLPurifier_Config::createDefault();
$config->set('Core.Encoding', 'UTF-8'); // replace with your encoding
$config->set('HTML.Doctype', 'XHTML 1.0 Strict'); // replace with your doctype
$config->set('HTML.SafeObject', true);
$config->set('HTML.SafeEmbed', true);
$purifier = new HTMLPurifier($config);
$about_me = mysqli_real_escape_string($mysqli, $purifier->purify($_POST['about_me']));