Firefox versions prior to Firefox 58 can use SQLite databases by using a special environment variable, so this isn't really something new. Only in Frefox 58 the SQLite format got enabled by default.

• NSS_DEFAULT_DB_TYPE="dbm" : key3.db - cert8.db
• NSS_DEFAULT_DB_TYPE="sql" : key4.db - cert9.db

Firefox 58+ will fallback to the older versions if you remove the newer SQLite versions. If you need to use the newer versions with older Firefox versions then try to start Firefox via a CMD file and set NSS_DEFAULT_DB_TYPE to sql.

• set NSS_DEFAULT_DB_TYPE=sql

See also:

• /questions/1011196 Migrate site and master passwords and logins from Firefox to Light

Thank you for responding, cor-el.

So does this mean Firefox 58 will not be able to share data with other Firefox versions?

Not unless you take the extra effort and use key4.db in the other versions as well. Support for SQLite key4.db and cert9.db is probably been available for 10 years or more.

ESR 10 already had it:

• https://dxr.mozilla.org/mozilla-esr10/search?q=regexp%3ANSS_DEFAULT_DB_TYPE

Yup, we're bound to start having millions of these issues now that the Password Exporter Add-On no longer functions with the new(est) Firefox. That extension has always been lagging behind, but somehow remained useful until recently.

I don't get how come that Mozilla hasn't included this (import, export) mechanism into the browser, or made their certified, official utility (in the past decade+)

Edit: The Sync component is, basically, bloatware - and something that Google Chrome, Android, or Apple users would like. For us, normal people, it's not really a solution, btw. :)