If it's just your addressbook, click to addressbook pane, highlight the addressbook, click the three dots to the right and select export in your choice of several formats. If your intent is to replace the addressbook on another PC with thunderbird, just copy the abook.sqlite and history.sqlite fron the profile and pasted into the receiving profile. That 2 gig limit is for the entire profile.

In addition, my desktop computer shows zero emails to my other two accounts, even though there are dozens of emails in those accounts that show on my laptop. I checked the settings and they are all correct. When I looked at my Comcast server, one of those other accounts shows my messages, but the other one does not. I will see if I can find the settings for that account on the server.

https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer