<?php
$title=urlencode('Title of Your iFrame Tab');
$url=urlencode('http://www.facebook.com/wordpressdesign');
$summary=urlencode('Custom message that summarizes what your tab is about, or just a simple message to tell people to check out your tab.');
$image=urlencode('http://www.yourdomain.com/images/share-thumbnail.jpg');
?>
https://www.facebook.com/sharer.php?s=100&p[title]=<?php echo $title;?>&p[summary]=<?php echo $summary;?>&p[url]=<?php echo $url; ?>&p[images][0]=<?php echo $image;?>