Hover the mouse over your name and then click on “Settings”, or access Settings using your touch screen.
Click on “Account Security” (on the left side of the screen).
Click on “Manage app passwords” (at the bottom of the screen, or scroll down to see it).
Click on “Select your app”.
Look at the list of apps and select yours if it is listed. Thunderbird is not on the list, so select “Other App”.
Type “Thunderbird” into the “Enter custom name” field.
Click on the “Generate” button.
Copy the password that is generated. Keep a record of it. You will need to use this new password every time you start Thunderbird, unless you use the Thunderbird master password to remember it.
Go to Thunderbird and click on “Get Messages”.
When Thunderbird asks for the password, enter the new app password that was generated by Yahoo.
The first time that you send mail, enter the same new password that was generated by Yahoo. This is for the outgoing mail server.
If Thunderbird does not ask for the new password and instead gives an error message, go to Thunderbird – Tools – Options – Security – Saved Passwords… and delete the old incoming and outgoing passwords for the relevant account.
After these steps, Thunderbird will be able to access your Verizon-Yahoo mail again! If you have more than one Verizon-Yahoo account, then repeat the procedure for each account.
I think this procedure will also work for Outlook, iPhone/iPad mail, and other email apps, but I have not tested it with anything other than Thunderbird.
The password created using this procedure is only for Thunderbird (or other email app selected in Steps 5-7). If you use the Yahoo app on a phone or tablet, or access webmail on Yahoo.com, your original Yahoo password will still be active on those other devices.