Do you mean that when you have "Address Book" open, the "Personal Address Book" is missing? Or is it present, but empty?

Immediately backup the Profile folder, just in case something else goes wrong.

1. Download the add-on: MoreFunctionsForAddressBook.  Click on that link and save the .xpi file to your computer.

2. Follow the instructions in Installing an Add-on in Thunderbird for "A slightly less ideal case", to install the add-on.

3. Restart Thunderbird.

4. Open your current Thunderbird Profile folder: Thunderbird menu: Help: Troubleshooting Information (If you cannot see the Thunderbird menu, press the Alt key or F10 key on your keyboard to show the menu) Under "Application Basics", beside "Profile Folder", click the "Show Profile" button. This will open a Windows Explorer window showing the contents of your Thunderbird Profile folder.

5. Quit Thunderbird, but leave that Windows Explorer window open.

6. Move (not copy), the file "abook.mab" to your desktop. If there are files with similar names like "abook-1.mab", or with other numbers, move them to your desktop. The numbered ones are backups that were made for some reason.

7. Start Thunderbird.

8. Open the Address Book.

9. Right-click "All Address Books", select "MoreFunctionsForAddressBook", then "Import addressbook from mab file".

10. Choose a name for the address book we are going to import.  Do not name it "Personal Address Book" or "Collected Addresses".  Those are special names.  This new address book will be temporary.

11. In the Addressbook import window that comes up, navigate to your Desktop folder, and choose the "abook.mab" file you previously saved there.

12. You will be prompted to restart Thunderbird to finish the import. You can repeat this import process for each abook file before quitting and restarting Thunderbird.

13. Once you have started Thunderbird again, open the Address Book, and look at the address book(s) you created and imported.  They should have all your contacts.  You can select them all and drag and drop them to "Personal Address Book" if you want.

Let me know how it goes.

Here's how I fixed the problem:

This problem is related to another issue that I had: https://support.mozilla.org/en-US/questions/1169200

I lost the extra address books that I had created when used MozBackup to restore a profile. I lost access to all my e-mail, calendar and most of my address book information. (It turns out that the latest version of MozBackup doesn't support the current version of Thunderbird.)

After the restore, all I had was my default address book and the collected addresses book. The ten or so other address books that I had created were gone. I found them in my profile folder. They all have .mab suffixes on the file names. The main address book is stored in abook.mab and the collected addresses are stored in history.mab. In addition to those I have impab.mab, impab-1.mab and abook-1.mab through abook-9.mab.

By using Thunderbird to create a new address book I was able to figure out how to get Thunderbird to recognize my old address books. It created abook-10.mab. Looking in prefs.js, I found these lines that were related to the new address book:

user_pref("ldap_2.servers.abook-10.description", "temp"); user_pref("ldap_2.servers.abook-10.dirType", 2); user_pref("ldap_2.servers.abook-10.filename", "abook-10.mab");

I then added the following 3 lines for each of the missing address books:

user_pref("ldap_2.servers.fname.description", "fname"); user_pref("ldap_2.servers.fname.dirType", 2); user_pref("ldap_2.servers.fname.filename", "fname.mab");

Where fname is the name of one of the .mab files associated with a missing address book. It's interesting to note that the three lines of code don't exist for the main address book or the collected address book.

Note that you have to exit Thunderbird before editing prefs.js. I used Windows 10 notepad to edit it. The .mab files are some sort of text files and can also be opened and viewed with notepad.

After editing the prefs.js and restarting Thunderbird, all the address books appeared on the Address Book pop-up. I right clicked each address book and used properties to change the name displayed for the address book. The address book name gets stored in the second parameter of the description preference. For example:

user_pref("ldap_2.servers.abook-1.description", "new name");

I hope this helps.

FYI: The Mozbackup author has the warning on his page to continue to use it at your own risk. It has issues and he is not going to fix hem.