Neither Thunderbird nor Mozilla are an email provider. You'll need to talk to your email provider, where you have your account.

THANKS SO MUCH ! I am such an end user.

I KNOW FULL WELL Thunderbird nor Mozilla are MY EMAIL PROVIDER!!! I just want to disable my CURRENT email address ON THUNDERBIRD while I create a new address with EARTHINK.NET. What should remove from Thunderbird right now to turn it off?

Since your question has nothing to do with what the thread owner asked you should probably start your own thread. The original owner seems pleased with their answer and marked it solved. They really do not want email letting them know you are asking unrelated questions on their solved thread.

You add or delete the info for your actually email provider, not Thunderbird, in Account Settings. At the very bottom of the listing on the left side of the Account Settings page is Account actions. Remove Account is there.