Sorry, yeah, that is a known issue in Firefox that we're trying to have resolved; it apparently cleans up ServiceWorkers/AppCaches that haven't been actively used recently. Was this your first time opening cyph.im, or had you used it in the past?
I have used it in the past, that's why I assumed my cached version was cleared.
Ah, cool, that makes more sense (I couldn't think of a reason for that to possibly happen on the first use, since at that point the pinned TLS key wouldn't yet have been invalidated).