To see folders on the Comcast mail server you'd need to be using IMAP in your mail client. This page: https://customer.comcast.com/help-and-support/internet/email-client-programs-with-xfinity-email/ suggests that they actually use and recommend it. If you look at the account settings in Thunderbird, it will say, under "Server Settings" what type of server you are currently using. If you are using IMAP, then check that all the missing folders are subscribed and set to synchronize. Look at "Synchronization & Storage" in Account Settings, and check under "Advanced" for the subscriptions. For your Contacts, I think you need to visit the Comcast webpage and look for an option to export your contacts. Options such as CSV ("comma separated values") and maybe vCard or vcf may be offered. CSV files can be imported straight into Thunderbird. vcf files can be used too, but may need an add-on. Look at "From somewhere else to Thunderbird:" here: http://chrisramsden.vfast.co.uk/11_Thunderbird_Settings_and_the_Profile.html