Help/More Troubleshooting, Profile Folder, Open Folder, close TB, delete or rename cert9.db, key4.db and logins.json. This will erase all saved passwords, and the files will be recreated when TB restarts. See if passwords are saved.

Check that there is no external password manager that is part of some security/antivirus app.

I have the same problem accessing Gmail, after upgrading Thunderbird. I tried the workaround above. The three files were recreated, but the app password wasn't saved. I tried switching to Oauth2, but the key wasn't saved, either. I'm back at "Normal/Password" level security with two-step authentication in Gmail, which is how I was set up before the Thunderbird upgrade. I am able to retrieve mail by manually entering the app password when prompted, every time I get mail. Not pretty.

I just discovered that I am also unable to send now, for lack of password connectivity. It doesn't work if I manually enter the app password. Any other ideas?

I have the same problem accessing Gmail, after upgrading Thunderbird. I tried the workaround above. The three files were recreated, but the app password wasn't saved. I tried switching to Oauth2, but the key wasn't saved, either. I'm back at "Normal/Password" level security with two-step authentication in Gmail, which is how I was set up before the Thunderbird upgrade. I am able to retrieve mail by manually entering the app password when prompted, every time I get mail. Not pretty. I just discovered that I am also unable to send now, for lack of password connectivity. It doesn't work if I manually enter the app password. Any other ideas?

Remove the entries from Saved Passwords in Preferences/Privacy & Security, and in the same section accept cookies, then set the incoming and outgoing authentication to OAuth2, restart TB, enter the account (not app) password in the OAuth window to allow access.

Thanks for your advice, sfhowes. I'm totally stuck, so it's great to have expert help.

I'm on TB level 91.4.1

I retried the OAuth2 as you specified, just in case I hadn't restarted TB between. The results were the same result as yesterday with OAuth2: The information isn't saved. Each time I click "Get mail", the Google sign in screen pops up, a message gets sent to my phone, and I need to confirm that I'm allowing TB access.

Still unable to send, even if I provide the password.

I'm changing back to "Normal/Password", which is less hassle to work around. Any other ideas?

There are millions of TB users with working gmail accounts, so as long as you have the correct settings, it should function without errors. Otherwise, you probably have some external app affecting the process, such as antivirus, VPN or a password manager that is part of some AV apps. If you're able to run Windows in safe mode with networking, that will bypass startup apps that might be interfering.

I would recommend you not use normal password/app password authentication, as OAuth2 is simpler and less likely to cause issues with authentication, 2-step verification etc.

Having the same problem. Older TB works fine. But when I transferred to a newer version on a new Win 10 system it won't save the passwords.

I've tried the file deletion work around but nothing changed. I've disabled my AV and VPN and still no change.

One additional piece of information, when I go into look at saved passwords it shows that I have none. (Thus the problem.) I thought that perhaps if I set a primary password it would force TB to reinitialize its password mechanism. But when I set the primary password it came back with "Can't set primary password" (or something similar.) So it would appear to me that there is something going on with your password management system.