In my case, and again using a dongle, with KLM, it loaded up the home page and from there when I tried to go to the 'booking' part it half loaded and then stuck. In order to see if the problem was with the website I called a friend who was a few miles from me but on an ADSL connection and asked him if he had the same problem, answer no.
I went somewhere where I could get onto a Wifi connection and it was fine, but as it was a public place I was nervous about using my credit card so was unable to finalise the booking.