Your TB profile folder is located by default here:

C:\Users\username\AppData\Roaming\Thunderbird\Profiles\8charstring.default

Allow the viewing of hidden files and folders.

The profile has 2 default address books: abook.mab (Personal Address Book) and history.mab (Collected Addresses). If you have these two files from your old profile, you can copy them into the profile (while TB is closed), overwriting the current files.

If you have other mab files, e.g. impab.mab, reply here for instructions on how to import them to TB (using MoreFunctionsForAddressBook).

Thank you. This all makes sense, but when I follow the instructions, I still have nothing in the address book. The .mab files are 8KB and 4KB so should not be empty, but when address book is opened there is nothing. Any other suggestions? I do appreciate your help.

Did you copy the mab files into the ...\Local\Thunderbird\Profiles\8charstring.default folder, instead of the correct ...\Roaming\Thunderbird\Profiles\8charstring.default folder? If the existing address books were empty, copying the old mab files into the wrong location would result in what you see. You should have seen a prompt asking if you want to replace the existing files.

Perhaps a picture will help. Thank you.

Move the mab files into r9ncj....default, if that is your current profile.

Thank you for your efforts. I now think I inadvertently copied over the files, rendering them blank.

I mistakenly changed the File "OPEN WITH" association to Windows Word. Now the .mab folders indicate that it Opens With Microsoft Office Word. I'm trying to get the file association back to the TB Default OPEN WITH association which I have NO Idea what that file asscociation is? None of these Support items offers any advice how to change the OPEN WITH file association repair. One TB page directed me to a menu, but the drop down menu did not show any Default options. So my lesson is to NEVER select Open With option as there is no UnDo or reversible file default option available to correct the mistake.

Sorry all, but I simply copied the file from my iMac and copied it into the W10 desktop and moved to the 8 digit folder and poof it worked! The file in the Apple OS is so simple to find without digging through Drive and Program listings of W10, that in the near future I will trust all of my Integrated devices to Apple OS. The W10 changeover is convoluted and not intuitive to know how to do what used to be simple operations. Good luck to all trying to work with that system! Ugh!

Clarification: 8 digit folder = 7skpvp0r.default

My computer crashed while updating windows 10 and I did not have a back up of Thunderbird addresses and emails. The computer place was able to restore all files. How do I restore my contacts and emails?