Darn! That's not an extension. That's a code I found that it maximizes the page height inside the FB canvas. However, I copied it from an other site of mine and I forgot to change the appID. I change it now, but still same behavior. This is the code:
<!-- Full size FB iframe page -->
<div id="fb-root"></div>
<script src="
connect.facebook.net/en_US/all.js">
<script>
FB.init({
appId : 244294882274400,
status : true, // check login status
cookie : true, // enable cookies to allow the server to access the session
xfbml : true// parse XFBML
});
FB.Canvas.setAutoResize(7);
</script>
<!-- End Full size FB iframe page -->