I'm getting the same error as https://news.ycombinator.com/item?id=32176165 (your previous post of this 19 days ago) so whatever needed fixing ain't fixed.
Sorry, don't want to make HN comments to be a GitHub issue tracker, but this info will help.
It looks like F.F. doesn't support IndexedDB in private mode at all: https://bugzilla.mozilla.org/show_bug.cgi?id=781982, and IndexedDB is the main data storage for okso.app.
If this is the case I'll think about some fallbacks, maybe to LocalStorage, to make the app work in such cases as well...