Hi @seewhy, thanks for the detailed report!
We did change to different infrastructure on the server in November (See ODK XLSForm Online v1.0), so that probably explains the change.
But, I've been able to try a basic form on Firefox 57 on macOS and Windows 10 and it works great for me.
Do you see the same screen that I'm seeing above? Can you try the basic form to see if that works?