Right-click an address book, Export..., choose csv format. But you could also add Contacts as a CardDAV address book, then copy contacts from other address books by drag and drop, while holding Ctrl.

Assuming the contacts are in the address book. What if you are trying to export them from all of the emails you just imported into Thunderbir from gmail!. I need to extract the contacts so that I can finally get to the step of exporting as CSV. But everyone says, "go to your address book." but no contacts are there.

Assuming the contacts are in the address book. What if you are trying to export them from all of the emails you just imported into Thunderbir from gmail!. I need to extract the contacts so that I can finally get to the step of exporting as CSV. But everyone says, "go to your address book." but no contacts are there.

To extract addresses from messages, try this add-on:

https://addons.thunderbird.net/en-us/thunderbird/addon/mail-extractor/