There is no Thunderbird password. The account you set up with your email provider requires a password. Check with your email provider about password recovery options.

ok. TB doesn't have a password. My mail comes to TB via gmail. I used THAT password and it still didn't take it. Actually I even changed the gmail (google) password and tried to create my TB account and it still says "username/password" don't match ? ????

See https://support.google.com/accounts/answer/6009563

What is your account type - POP or IMAP?

It was POP ... and when I select that, that 'not valid' message instantly appears. When I click the IMAP it goes into la-la land and after about 5 minutes I just cancel out.

With POP you'll need to 'allow less secure apps' as per the instructions in the Google support article linked above.

With IMAP make sure the 'Authentication type' is set to 'OAuth2'. The same goes for the outgoing server (SMTP).

In any case, you'll need a valid password. If your old password is lost, check with Google about password recovery options.

You've been a great help .. I've moved forward a bit with getting TB back. To my knowledge nothing has changed except time - a week or so .. but my password worked this time (sorta) but the window that appeared had the message in the middle saying "configuration could not be verified - is the name or password wrong?" I clicked "done" - and the 'Add Security' Exception' window appeared listing 'pop.gmail.com995' as the exception to add. On my gmail settings that I had previously printed out, the server name IS pop.gmail.com. the port IS 995 (as is the default 995). Should I add this 'exception?' p

Should I add this 'exception?'

You shouldn't. Here is why. https://support.mozilla.org/kb/add-security-exception

Please post a screenshot of the error. https://support.mozilla.org/kb/how-do-i-create-screenshot-my-problem