Check your firewall and see if Thunderbird got blocked due to the update. This has happened for other users.

Do you get any error messages?

Mozilla is connecting to Comcast.net ,but does not load the emails. I've check the mail ans server settings in the Mozilla tools section.

Have you disabled email scanning in your anti virus program and as it is comcast and they give you nortons go into nortons and make sure it explicitly allows all Thunderbird access to the internet a setting of Automatic is not adequate.