I'm using the following code for my like button
<fb:like id="facebook-like" href="http://mysite.com/index.php" layout="button_count" width="450" show_faces="false" font=""></fb:like>
Some users have experienced the like button not showing up. Noted in 3.6.17 but observed in other versions. I'm somewhat familier with the firefox iframe bug, but I was currious if anyone has any work arounds for the facebook like button.