OK, had a look. It is not the problem you referred to above, as that completely blocked IE11 browsers from displaying anything.
Looking at the details in firebug I see there is a problem with his language file (Danish). The translation “Afspil” seems to be breaking the slide show function in the random media block. It will probably be the old double-quotes issue I suspect.
I can’t test for that, but try giving him an updated .mo file and see if it helps.