Just gave it a run through on Firefox 68.0.2 without a problem so that’s certainly not it.
Have you tried to login using the credentials you provided? Would be interesting to know if the account got created and it was the interface that failed. You could also try the “Forgot password” button on the login page which will email you and state whether your account exists or not.
If that hasn’t worked it would be good to go through the sign up again, and see if any error messages are being sent to the browser console. For Firefox you can open this with (Ctrl+Shift+K).
Apologies that this is happening, its not something I’ve seen before so hope we can get it resolved quickly.