Currently, if you attempt to open the registration page in a browser that doesn't support the service worker API or where the service worker API is disabled (e.g., in private mode) the registration page will not load. In the console, I see this exception:
Uncaught DOMException: The operation is insecure. openmrs.js:2
We've also seen this error reported:
Uncaught (in promise) Error: Registering the Service Worker is not possible due to missing browser capabilities.