"If is first post" within a plugin PHP code

[kh99]

That hook is called before the isfirstshown is set, but you can use this:

if ($counter == 1 AND $fetchtype == 'post' AND $post['visible'] == 1)
{
}

Also, that hook is called froom some scripts other than showthread (newreply.php, editpost.php, comments.php). The above might work because $fetchtype is probably not set in the other scripts, but you could add THIS_SCRIPT == 'showthread' to be safe.