Can you get access to your webmail account using a browser ?

I did not save my password and I do not know how to log onto my account without knowing my new password. Is there a way to work around this? Sorry for the late response.

yes there is a way! Contact ATt and have them reset your password again to something you do know.

If you cannot logon to your webmail account because you do not know password, then it is impossible for Thunderbird to get access without the correct password.

Passwords can only be created in the webmail account accessed via a browser. When trying to logon there is usually a 'Forgotten Password' type of link which you can use. Then follow the instructions in that link in order to get access again. The only other alternative is to contact the people with whom you have an account. That being AT&T. They will probably have you jumping through a few hoops because after all you need to prove you really are you. Then they will give you a password. The first thing you do is use that password to logon to your webmail account, where you will need to update that password to a new password. Log out of webmail, wait long enough to have a cup of tea and then logon to webmail account using the new password to check it gets you access.

Once this is achieved then use that new password in Thunderbird when prompted.