I would suggest since you have it turned off to just go ahead and remove sll zlimbox files from your server, remove any sql it might have had you install then reupload all the files for lightbox, this will make sure you have all the files where they should be. I use this on 1.3.9h stores all the time...my own and those I install for others and the buttons appear when additional images are available, in Firefox, IE, Chrome, Safari,

Also make sure you have it set to show the buttons in admin.