According to https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/WebExtensions/API/storage i should not use the storage API to save confidential data. There is a warning on that page:
The storage area is not encrypted and shouldn’t be used for storing confidential user information.
I can understand that warning, since the data isn’t encrypted there. But on that page, there is no hint, what we should instead of the storage API. Can someone here please recommend an alternative?