After a lot of time wasted on checking and rechecking the block visibility settings, I found that the comment block has been hard-coded to not work on anything other than nodes.

// in fb_social_comments.module
case 'view' :
switch ($delta) {
case 'comments' :
// show the block comment only for nodes
$node = menu_get_object();
if (is_object($node) && $node->status && $node->nid && arg(2) != "edit") {

I would like my users to be able to comment on views as well.
Especially since all the other blocks work fine on views.

Is there any particular reason for this deviation from the normal block behaviour?