How is Mozilla being breached different from them going rogue?
A more pedestrian failure mode that occurred to me would be a simple bug, or a configuration format change causing the URL of my private sync server to be ignored. If using Mozilla auth, this would cause my data to simply be silently uploaded to Mozilla's sync server -- and I'd be unlikely to find out about it until much later. If not, it would likely cause an authentication error instead.
A more pedestrian failure mode that occurred to me would be a simple bug, or a configuration format change causing the URL of my private sync server to be ignored. If using Mozilla auth, this would cause my data to simply be silently uploaded to Mozilla's sync server -- and I'd be unlikely to find out about it until much later. If not, it would likely cause an authentication error instead.