Unable to log in even after changing password as instructed.

What instructions, and from whom?

What prevents you from logging in? Is there any error message?

Also see https://support.mozilla.org/kb/cannot-receive-messages

Instructions were from Google, as stated.

Error  message  says " login to server IMAP.Gmail.com  with username.  Gene congdon@gmail.com failed"

Please re-read my original explanation message also.

Unable to log in even after changing password as instructed.

I don't see any request for you to change your password. So why did you attempt to change the password in the first place?

Please re-read my original explanation message also.

I did. Here's another question:

After making copy of Google data

What does this mean exactly?

Also, please post your Troubleshooting Information. At the top right of the Thunderbird window, click the menu button , then select Help > Troubleshooting Information. Press the "Copy text to clipboard button" and paste the information into your reply.

1. I was asked to create new password by Thunderbird when it no longer wanted to open following the action I took to comply with the Google notice (since certain old data would no longer be available at a soon date it would be wise to copy all that info if I needed it, which I chose to do). This may/may not have any direct bearing on the problem I now face trying to connect with the Google IMAP mail server.

2. As long as I am unable to log into Thunderbird I am also not able to use the clipboard.

3. The following info might be of some help.... just in case.

   Name: Thunderbird
   Version: 60.6.0
   Build ID: 20190314112142

   Update Channel: release
   User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:60.0) Gecko/20100101 Thunderbird/60.6.0
   OS: Darwin 17.7.0

   Multiprocess Windows: 0/0 (Disabled)
   Web Content Processes:
   Stylo: content = true (enabled by default), chrome = true (enabled by default)
   Enterprise Policies:
   Google Location Service Key: Missing
   Google SafeBrowsing Key: Missing
   Mozilla Location Service Key: Missing
   Safe Mode: false

 Mail and News Accounts
   account1:
     INCOMING: account1, , (none) Local Folders, plain, passwordCleartext

   account2:
     INCOMING: account2, , (imap) imap.gmail.com:993, SSL, passwordCleartext
     OUTGOING: , smtp.gmail.com:465, SSL, passwordCleartext, true

 Crash Reports for the Last 3 Days

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I was asked to create new password by Thunderbird

Thunderbird doesn't have any account passwords. All it can do is to remember your account password, so that you don't have to type it again and egai every time it's needed. In order to change your account password you'd need to login to your account with a web browser, and change it on the server.

Is this what you did? If not, what exactly did you do?

... the action I took to comply with the Google notice (since certain old data would no longer be available at a soon date it would be wise to copy all that info if I needed it, which I chose to do).

That sounds very odd to me. Are you certain that was a legitimate request from Google, and not some sort of malware? Google usually does not want to remove your stuff from the server, and they have plenty of storage space.

For IMAP (incoming) and SMTP (outgoing) servers set the 'Authentication type' to 'OAuth2' in your Thunderbird account settings.

Sounds like you are talking about Google shutting down Google Plus and their app called Inbox. None of this has anything to do with Thunderbird or your email.