webpage is xyz.de
open all other non “xyz.de” pages in lightbox.
add a exclusion list to exclude external pages to open in lightbox.
May open excluded links in new window.
allow to exclude whole domains.
sometimes it is also good to have only a include list to specify which links to open in lightbox.
PS: one idea set a minimal screen size to open external pages in lightbox.
so on a iphone 4 open only in second tab not in lightbox.