Beispielcode:
<a onClick="aussen.setInnerFBML(azu);" style="cursor: pointer;"><h1>Klick, um iFrame anzuzeigen!</h1></a>

<div id="aussen">
</div>

<fb:js-string var="azu">
<fb:iframe height="500" allowTransparency="true" frameborder="0" scrolling="no" style="width:100%; border:none" src="http://www.facebook-landing-page.de"></fb:iframe>
</fb:js-string>

<script type="text/javascript" charset="utf-8">
var aussen = document.getElementById('aussen');
</script>