$re = '/(?:.+(?:\/|%2F))+?([^\/]+\.jpg)(?=\?)/m';
$str = 'https://firebasestorage.googleapis.com/v0/b/work-52105.appspot.com/o/user%2FwCBsmRGAxbMQXO2yqc8jF65pmIG3%2FDepositphotos_59984669_s-2015.jpg?alt=media&token=916f8bb6-2ccf-4a95-b76b-814db081c028';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php