To all, some of the advice I got was spot on.
I've been able to recover my address book, and I learned a lot at the same time.
So, to all, a big thanks.
A good thought if I can get it to work.
I think the sqlitebrowser is beyond me, but I tried the other suggestion.
It came back to me saying the program doesn’t exist. So I figured out that it wanted me to install nemo. Installed that and nautilus for good measure.
So the installations appeared...
I have a SSD on which I had my OS, Linux Mint 20.
Also had Thunderbird.
The operative word here is had.
The SSD crashed and obviously could not be accessed by the OS.
I am able to access files using a live CD or another installation.
I had a backup of the disk through the Linux backup tool...