に以下を記述

<script type="text/javascript" src="http://connect.facebook.net/en_US/all.js"></script>
<script language="JavaScript">
FB.init({
  appId: '1235678910', // App ID/API Key
  status: true,
  cookie: true,
  xfbml: true
});
 
window.fbAsyncInit = function() {
  FB.Canvas.setAutoGrow();
}
function sizeChangeCallback() {
  FB.Canvas.setAutoGrow();
}
</script>

の直前に以下を記述
<div id="fb-root"></div>
<script>
 FB.Canvas.setAutoGrow({ width: 810, height: 2000 });
</script>