Now getting this error instead of the one above when I try to add any Gmail account to Thunderbird:

Component returned failure code: 0x80550014 [nslMsgIncomingServer.verifyLogon]

"Uninstalled" (I guess ... apparently that doesn't mean "Uninstall" but more like "hide my icons and pretend to be uninstalled" :D ) Thunderbird and re-installed it (download new copy of the same version)

After "re-installing" it the same accounts I had set up in the previous copy re-appeared behaving the same as before ... every account except the Gmail account was working fine, Gmail account seemed to not even be able to connect. Removed the Gmail account, tried to add it again, as before. Screenshot kept spinning for over 2 minutes before I canceled the attempt.

Meanwhile, I have continuous successful access to the Gmail account in my web browser. Also noting that, before I started removing and re-adding the Gmail account in Thunderbird I had no problem reading any of the messages displayed via my IMAP connection, even as Thunderbird could not authorize to get new messages ... which I saw successfully come into the account via my browser(s).

I hope this helps. Thanks, again.

Please note - if you have switched on 2 step verification in the gmail web account then switch it off and do not use any app specific password.

If you have anything using localhost such as Apache Xampp (people use it when managing websites) then you must switch it off until oauth is set up.

You must have the following : Thunderbird

• Settings > Privacy & Security

WEb Content

• Select 'Accept cookies from sites'
• Accept third party cookies 'Always
• click on 'Exceptions'
• Add this as an 'allowed' exception : https://accounts.google.com
• click on 'Save Changes'

• Scroll down to Passwords section
• click on 'Saved Passwords'
• Click on 'Show Passwords'

If you get a 'Windows Security' window asking for password - enter the same password you enter when you start computer and logon to User Account to see desktop etc. It's not talking about a mail account password.

Completely clear any password to do with that gmail account. click on 'Close'

Then restart Thunderbird.

New > Exisiting mail account Enter name, email address and normal password Click on Continue Server settings should be auto located and set up to use OAuth2.

When you click on Done You should be prompted by gmail to allow Thunderbird access which you need to complete.

Thank you for your reply, Toad-Hall.

I have executed each of the steps you suggested but still no joy. See attached for settings from the latest attempt.

I note that the password is not being saved in Saved Passwords. During my original troubleshooting (as above) I cleared out the Saved Passwords where it WAS saved, but it has not been saved in any of my attempts since, despite consistently clicking "Allow" in the "Allow/Deny" prompt modal (screenshot attached).

Incidentally in this version of Thunderbird there is no option for "Existing mail account". I can do: File > New... > Email account... or Tools > Account Settings > Account Actions > Add Mail Account... both with the same result.

I really appreciate you taking the time to consider this issue. It literally just suddenly stopped working a few days ago with no changes made by me to any of my accounts after working fine for years. I have downloaded a fresh copy of the app, "uninstalled" the old one (as above) and re-installed the same version, as above.

Resolved with an earlier reply from Toad-Hall to another user: https://support.mozilla.org/en-US/questions/1379677