This is a very well known problem with firmware 1.31. In order to configure that page, you must use (any version of) IE. It will just appear blank in Firefox and Chrome.
D-link has fixed this problem in firmware 1.40, but for some reason they have been sitting on it for about 6 months now and haven't released it to the masses. I shake my head wondering what goes on in companies like D-Link (and TomTom) that cause such simple problems like this to linger for so long without them seemly doing anything about it.
If you're interested, you can download 1.40 from D-Link Taiwan support site here:
http://tsd.dlink.com.tw/
jB