Where did you save the profile prior to the reinstall? The addressbook would be there.

I didn't intentionally save it prior to reinstall. I didn't have the opportunity to do so. Windows failed, and I couldn't get on to do so.

Does FF/TB automatically save it to your profile? If not, that's stupid. I should be able to sign in to TB and have it populate.

The addressbook and account data are in the profile, but it is up to the user to do backups. Thunderbird does not have a cloud where it keeps copies of user accounts. There are such services, but there is a fee for them.

Thank you for this. That at least answers whether or not they're retrievable at this point.

I'm thinking seriously of switching out of TB....I get privacy, but I also need auto backups of information.

I know eM Client does a nice backup, but it's to the hard drive. Mailbird doesn't offer one that I'm aware of. TheBat! has a nice autobackup feature, but I don't recall if it's to the cloud or the same hard drive. You might pursue something such as Idrive, which offers a very low fee for daily backups, but you must first define the folders to be backed up (up to 5 gig is free) - and I've had great success with them for years. And there are others... BUT, I regularly see automated backups fail on this forum, mostly because they are done while Thunderbird is running and it has hold of the files so resulting backups are corrupted. If you pursue that route, I encourage setting the auto backup to run during time when you're not using thunderbird.