Your router (firewall) possibly.
They could; but I have not checked recently about Verizon FiOS, usually 443 is still allowed.
Presently nobody from the Internet can access your website due to the ports being filtered.
You could, however certificates expire in 90 days and recommend being renewed every 60 days.
There is the DNS-01 challenge which does not need to access Port 80.
Here is a list DNS providers who easily integrate with Let's Encrypt DNS validation