Delete these 3 files, logins.json, key4.db, cert9.db, to erase all account and master passwords, with TB closed, then restart TB and enter the passwords when prompted, check the box to have them stored, and see if they appear in Saved Passwords. Check that you don't have a password manager supplied by some security suites acting on TB.

sfhowes

Many thanks.

Seconds before your reply arrived I uninstalled Thunderbird and deleted the whole of the "thunderbird" folder in:

 users/USERNAME/appdata/roaming/

I then reinstalled Thunderbird and it worked!

Conclusion: it was stuff left over from a very old version of Thunderbird.

Many thanks for taking the time to reply.

Yes, it works to do a clean reinstall. However, that loses all previous email. For me that is a show stopper. I've tried the deletion of several files that seems to have worked for some people. Not me. Someone somewhere must know what's going on here.

Yes, it works to do a clean reinstall. However, that loses all previous email. For me that is a show stopper. I've tried the deletion of several files that seems to have worked for some people. Not me. Someone somewhere must know what's going on here.

You don't have to remove your current profile. Create a new one from Help/More Troubleshooting, about:profiles, add an account, and see if passwords work as expected. Data can be copied from the old profile to the new if necessary, and either profile can be launched from about:profiles.