I did, but seems I missed the actual subfolder where the databases are saved. But this makes it even worse. They all have sqlite installed, but offer not API for making use of it. Really missed chance.

Presumably GP meant Mozilla agitated for a Document/KV-store, yet for some inexlicable reason, in their own browser, they chose to implement IndexedDB with SQLite.

They could have used an actual KV store behind it, like chromium did (levelDB IIRC).