I know the settings are correct because Thunderbird originally left out Yahoo in the server names. A Verizon tech support actually corrected this for me remotely a couple weeks ago after I installed Thunderbird on my new laptop.
That said, I am now getting all of my email. Thunderbird had stopped asking for my password for several days. Don't know why. It just began to connect with the server immediately but never obtained any messages. Then, out of the blue, things went back to normal. When I actually enter my password, everything works normally. Still don't understand what was going on. But things are okay now. No need for drastic measures. Thanks for your feedback.