## comment.rb (remove the 'unless' condition & ID comparison...)

self.newsfeed.permissions.notifiable_for_comments(self.id).each { |permission|

    Mailer.deliver_comment_notification(permission.user, self)
  }

## permission.rb (...and put it in to the named scope)

  named_scope :notifiable_for_comments, lambda {|userid|
    {:conditions => ['user_id != ? AND status = ? AND comment_notifications = ?', userid, true, true]}
  }