The white screen was caused by an incorrect URL. The correct beta UI URL is: https://betaui.opensprinkler.com/js.
Furthermore, this issue was resolved without the need for using the beta. The underlying issue was FireFox complaining of a weak self-signed certificate. The secondary issue was the Javascript URL used by OpenSprinkler was non-secure by default and caused an issue when the primary site being accessed is using SSL.
Thanks