functions.php

<?php
/**
 *  Add Facebook SDK
 * 
 */
function be_facebook_sdk() {
  ?>
<div id="fb-root"></div>
<script>(function(d, s, id) {
  var js, fjs = d.getElementsByTagName(s)[0];
  if (d.getElementById(id)) return;
  js = d.createElement(s); js.id = id;
  js.src = "//connect.facebook.net/en_US/sdk.js#xfbml=1&version=v2.5&appId=123456789123456";
  fjs.parentNode.insertBefore(js, fjs);
}(document, 'script', 'facebook-jssdk'));</script>  
  <?php
  
}
add_action( 'genesis_before', 'be_facebook_sdk' );