Magnus, FYI, I think this bug shouldn't be responsible for scenarios where stored passwords cannot be read. Unusable stored passwords could be seen it key4.db doesn't contain the symmetric key used for decrypting logins.json. For the scenario handled in this bug (as caused by the code that was backed out in bug 1790605), if file logins.json already existed, file key4.db was not copied. In other words, this bug here only affected users who did not yet have saved passwords. (It affected openpgp key storage, it did not affected stored passwords.)
Bug 1790610 Comment 44 Edit History
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Magnus, FYI, I think this bug shouldn't be responsible for scenarios where stored passwords cannot be read. Unusable stored passwords could be seen it key4.db doesn't contain the symmetric key used for decrypting logins.json. For the scenario handled in this bug (as caused by the code that was backed out in bug 1790605), if file logins.json already existed, file key4.db was not copied. In other words, this bug here only affected users who did not yet have saved passwords. (It affected openpgp and s/mime key storage, it did not affected stored passwords.)