This addon is a plugin. You need to extract it to your /plugins folder to install it.
Adds a notification about the comment author's status.Shows a colored icon if the author is online and a gray icon if offline. Before you activate this extension,you will require to add " .'<span>IsOnline</span>' "(without double quote)to themes/comments.php in line no.95 before the semi-colon(;), since the notification is to be added after the datetime.