Chatterbox doesn't work on private tabs on FireFox

[Half-Shot]

no persisted storage, database can be evicted by browser [vendor.7c61eada.js:3:46921](https://chatterbox.hss.element.io/assets/vendor.7c61eada.js)
Uncaught (in promise) Error: load failed: IDBRequest failed on .: (name: InvalidStateError) (code: 11) A mutation operation was attempted on a database that did not allow mutations.
    login https://chatterbox.hss.element.io/assets/main.67b6c3b0.js:1
[main.67b6c3b0.js:1:3822](https://chatterbox.hss.element.io/assets/main.67b6c3b0.js)

[MidhunSureshR]

Hydrogen depends critically on indexedDB which firefox does not support in private mode. So either firefox fixes this on their part (tracked here) or Hydrogen will need an in-memory equivalent to indexedDB.

[bwindels]

Perhaps in the short term we can show an error (or hide the UI completely) when window.indexedDB is not present and say it does not work in private mode for now.