I think this is confused enough here that it would help to have you post the images of your current settings again, since they don’t seem to match the other pictures posted. From what you have said:

Thunderbird settings should show
incoming.yahoo.verizon.net
port 110
Connection security none
authentication password transmitted insecurely

Avast! settings should show
yahoo.verizon.net pop3 110 none

Is this correct currently? This is simply an unencrypted pop3 email server?