You may bet everyone else reading this is wondering the same… Ah! You said in the the title of the post… OK :)

Is the Address Book the only thing that was affected in Thunderbird? Check the following article in case it's relevant to you:

https://support.mozilla.org/kb/recover-user-data-missing-after-thunderbird-update

The article did not provide me with anything helpful to this issue. Are you saying that EVERYONE has lost their address book?

No, I'm saying that something that might explain this could be that Thunderbird is using a different profile for some reason, but then I would expect you to miss more things, not just the Address Book, hence the question I asked.

If you do a search in the c:\users\<yourid>\appdata\roaming\thunderbird\profiles folder, you may find abook.sqlite and history.sqlite. These are the technical filenames of the addresssbook and the collected addressbook. You can import them with tools>import>importfromafile. This sometimes happens, that thunderbird creates a new profile and some content is left behind. No, this does not happen to everyone and is likely a glitch wherein an update was interrupted by another program, such as an antivirus product.

Yes, I have lost more than addresses. My history is missing as well as local folders. I thought I had risks well covered by doing regular backups to a local drive with Acronis True Image, and remote backups with Carbonite, but so far I have been unable to successfully recover the missing data.

It makes me irritated . . . was there no adult in the room when the latest release went out? Why wasn't an automatic backup of Thunderbird not made? Why was there no notice that gave an option of whether to proceed with the update? Why can't I go back to the previous version (which would assume a backup was made, I guess!!)

Your response is confusing. If you do regular backups with Acronis, a copy of your addressbook should be there. Thunderbird offers the option to allow automatic update or to do so only with your permission ( see setting>general). Did you check in profiles folder for abook.sqlite and history.sqlite? We are users, just as your are. We don't write the code or design features; we're here to assist. I think you will find them there and the tools>import>import from a file will restore them.

Well, this is looking more and more like the article I linked is relevant to you, since nowhere have you made any mention to having checked whether all your data could be in some other profile…