wp_login_failed only working on firefox

This has got me stumped.

I’m using the following code in the functions file to redirect a front end login attempt if details are incorrect. It’s working perfectly on Firefox, but doesn’t seem to be working at all on any other browser. Anyone have any ideas??

add_action( 'wp_login_failed', 'login_fail' );  // hook failed login
function login_fail( $username ) {
     $referrer = $_SERVER['HTTP_REFERER'];  // where did the post submission come from?
     // if there's a valid referrer, and it's not the default log-in screen
     if ( !empty($referrer) && !strstr($referrer,'wp-login') && !strstr($referrer,'wp-admin') ) {
          wp_redirect(home_url() . '/my-account?login=failed' );
          exit;
     }
}