On a Mac laptop (also using safari) I initially had the same issue as the iPad, in that the username and password boxes don't show. I checked the FAQ at the beginning of this thread, and I don't have McAfee (I have Norton, but that isn't on the iPad). I cleared cookies, and now the blue arrows don't show up at all on the Mac. I also tried both Chrome and Firefox, and no blue arrows; and if I select the downloader from the settings icon, it is again a blank page. I am at a bit of a loss and not sure if the issue is with my account or something on my end.
ETA - it seems to be an internet issue at home on my end. I could hotspot the iPad to a phone and the downloader box would show. I changed the DNS server settings on the iPad and this seemed to work. Weird. If anyone knows why this would be blocking the downloader, and a permanent solution, I would appreciate it. I will use the google DNS settings for now when I want to download.