Note that the Primary Password to login to the Password Manager (Lockwise) is local for each profile (each device has its own PP) and isn't transferred via Sync. If you use Sync then you merely login on each device to the same Firefox account using the email and password for this Firefox Account used for Sync.

If both devices are desktop devices (i.e. not mobile devices) then you can possibly use a removable USB drive to transfer the files directly from the profile on the old device to the profile on the new device. For the logins this involves copying two file logins.json (encrypted logins) and key4.db (key file stores the encryption key and possibly the Primary Password). logins.json and key4.db need to match to be able to decrypt the logins stored in logins.json.

You can use the button on the "Help -> Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page.

• Help -> Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

You can copy certain files with Firefox closed to the current profile folder to transfer or recover personal data. Note that best is to avoid copying a full profile folder.

• bookmarks and history: places.sqlite
• favicons: favicons.sqlite
• bookmark backups: compressed .jsonlz4 JSON backups in the bookmarkbackups folder
• cookies.sqlite for the Cookies
• formhistory.sqlite for saved autocomplete Form Data
• logins.json (encrypted logins;32+) and key4.db (decryption key;58+) for Passwords saved in the Password Manager
  key3.db support ended in 73+; to use key3.db in 58-72, make sure to remove key4.db
• cert9.db (58+) for (intermediate) certificates stored in the Certificate Manager
• persdict.dat for words added to the spell checker dictionary
• permissions.sqlite for Permissions and possibly content-prefs.sqlite for other website specific data (Site Preferences)
• sessionstore.jsonlz4 for open tabs and pinned tabs (see also the sessionstore-backups folder)

Thanks for the reply, which may be comprehensible to someone with a degree in computer science bot not very useful otherwise. I did eventually figure out that the password recovery process worked, even though I knew my master password and should not have needed to recover it to begin with. If you are stuck in the same limbo I was stuck in, be aware that the warning about recovering the account also erasing all the saved passwords is incorrect. I found a thread that noted that the erased passwords would be only if there were already synched passwords between accounts. I successfully recovered my account without losing any passwords, although since I knew the correct master password to begin with, it is unclear why it didn't just work in the first place. So, again, even if you know your master password, if you can't make the sync work, you could try to recover the account, and just ignore the warning that the passwords will be erased, they won't be erased, at least mine weren't .

Sounds there was a problem with the logins.json file and using password recovery used the logins-backup.json that current releases can use as a backup in such a case.