JOINできないのこんな感じで。

$params = array(
	'method' => 'fql.multiquery',
	'queries' => array(
		'q1' => 'SELECT uid2 FROM friend WHERE uid1 = me() limit 10',
		'q2' => 'SELECT url FROM profile_pic WHERE id IN (SELECT uid2 FROM #q1)'
	)
);
$facebook->api($params);