I have twice created a new address book, but when I return to Thunderbird the next day the address book has disappeared

Is Thunderbird closing completely? Check task managed for a running instance

Create the address book how? is the next obvious thing as there is more than one way to do just about everything in Thunderbird.

Are any other changes lost on restart?

Thanks, Matt To create while in Address Book, I click on the icon in the upper left corner "Create new address book" which provides a drop down menu with 3 options. The first option, which I select, is "Add Local Address Book." Selecting that, I get a form with a box to type the new local address book name. I do so, click on OK and the new named address book is added to my list of local address books. I either manually enter various addresses or drag and drop addresses from other existing address books. That new local address book and the addresses function as long as I don't close Thunderbird. However, once I close Thunderbird, when I reopen Thunderbird, the newly created local address book and the address I have added have vanished. The addresses I copied from other address books still remain in the original address books.

I can go into an existing address book and enter manually or drag and drop existing addresses and they remain after a close/restart. However, if I rename that existing address book, the original address book name will reappear on a close/restart and the rename name will have disappeared.

As far as I know there are no other changes lost on close/restart.

I just closed Thunderbird and it disappeared from Task Manager. When I reopened Thunderbird, it reappeared in Task Manager.

A puzzle. I hope there is a simple solution...and that you know what it is! ;-)

As Matt indicated, there may be other issues. From what you describe, the issue is that Thunderbird is not saving settings at shut down. Settings are saved in the file, prefs.js. If that file is prevented from updating, such as by an antivirus or VPN, then on restart, the changes aren't there. Identifying why the file isn't saved will probably resolve your issue. You can review this by

1. clicking help>troubleshootinginformation
2. scroll to 'profile folder' and click 'open folder'
3. you are now in the profile. is there just one prefs.js, or many (such as prefs-1.js, prefs-2.js, etc.) OR, if just one, is it set for 'read only'?

Please share what you find.