Maybe consider to enable the Password Manager temporarily once to store the Sync credential and disable the Password Manager once this has been completed to make Firefox create the chrome://FirefoxAccounts entry that stores the credentials in JSON format.

• Tools > Options > Security: Passwords: "Remember passwords for sites"

Thank you. That works, but only temporarily. I enable PW Manager and check that the password has been stored. It works for a few reboots over several days, but then the password no longer is stored, and I must start all over again. I've tried this repeatedly.

The password should be stored unless you remove it from the Password Manager, possibly by clearing passwords via "Clear history when Firefox closes".

Do you have any cleanup or security software that could be causing this?

Thanks. I am running CCleaner 5.07, but the option to delete Firefox saved passwords is not checked.

Hey Jimmy, visit about:sync-log from your url bar and copy and paste the 1st log you see there here.

It should contain information about the failed Sync and hopefully give some clues as to what's going on.

Well, I think that cor-el was correct. I went back and checked each of my systems, and it's only one that had the issue. I re-checked CCleaner on the unit, and it was in fact set to remove passwords. My fault. Sorry, and thanks very much for the help! At least I now know the cause.

You're welcome.