Adding Firefox and all my bookmarks to a laptop!
I tried with both computers on to do as the site suggests. To no avail. The bookmarks downloaded but not the passwords!
Are you copying the data or what?
logins.json and key3.db [v58+]key4.db : These are the password files. Copy Both !
Is your question related to Sync / a Firefox Account?
And if so, are you using the Master Password feature?
If so, did you enable that on the second device?