I tried over several days this week to book a new reservation, at different times during the day, after clearing cache, with 3 different browsers, including Chrome (normal and Incognitio mode), Firefox, and Microsoft Edge. Got the seven dwarves error screen every time. It didn't work for me until I tried at 1 AM Eastern time one day. This happened to be on Safari/iPhone, but when I tested that same combination the next day it was back to the seven dwarves error screen.
With all my attempts I'm convinced the problems are due to high website load, not any particular browser.
I only have trouble trying to book a new reservation. The Modify option seems to work most of the time.