Repetier-Firmware has no web frontend, so what are you normally showing there and which version? Also which browser are you using? Does it also happen on a chrome browser on your pc? There it woudl be easy to check javascript console to see what was going on. After all it looks like the browser windows crashed, so question is if there is something that crashes it and if you have e,g. enough memory on the device to show that because some webpages can need quite some memory.