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Well you really have to try the setup as I have suggested in both thunderbird and the avast SSL accounts for verizon.yahoo.net at the same time:
Tbird: POP3 port 110 connection security None.
avast SSL accounts: POP3 port 995 and SSL

Now that should in theory work and you should be able to download your verizon email (POP3)

I have a BTinternet emai account (amongst my others), yet there is no entry for this in the avast SSL accounts, this is because Yahoo handles all of the email for BTinternet, I don’t know if this is the same for Verizon.

So I don't know if you even need the verizon.yahoo.net entry in the avast SSL accounts as the sending and collection of that mail would go through the Yahoo mail and it is this which is reflected in the avast SSL accounts settings. If the above @@@@ settings when set at the same time doesn't work you could try deleting the entry for verizon.yahoo.net (reboot and see if avast resets it or not) and see if that works.