Are you still able to use the old Windows XP computer? If so, then you can export your Address Book(s) from it:

Thunderbird menu: Tools: Address Book Address Book menu: Tools: Export... Export to file type LDIF, save the file to a USB flash memory stick.

Export each Address Book, but don't name the "Personal Address Book" and "Collected Addresses" that way, give it other names. That way when it is imported onto the new computer, you will not have two with that name.

On the new computer: Thunderbird menu: Tools: Address Book Address Book menu: Tools: Import... Select "Address Books" and click "Next" Select "Text file (LDIF, .tab, .csv, .txt)" and click "Next" Choose the file(s) from the USB flash memory stick.

If you cannot use your old Windows XP machine and want to find the address book files from the external drive:

See: Moving address books between profiles

To locate the Thunderbird Profile folder in Windows XP: C:\Documents and Settings\***Username***\Application Data\Thunderbird\Profiles\ Replace C: with the correct drive letter. Replace ***Username*** with the correct username used in Windows XP. Under the "Profiles" folder you will probably see only one folder, which is the Thunderbird Profile you were using in Windows XP. If there is more than one, then look at the most recent one by date. If you are disallowed access to the folders, then you will need to change the permissions in Windows for the folders. Ask if you need help with that.

To locate the Thunderbird Profile folder in Windows 10: C:\Users\***Username***\AppData\Roaming\Thunderbird\Profiles\ There should be only one folder under "Profiles".

Thank you very very much. The old system is inoperative so I had to follow the second set of procedures and, after a cigarette or two, I finally did it correctly and now it has all the addresses. Again Thank You & Happy New Year.

Glad to here it. Please mark the question as solved.