One of my "Randy-isms" is "Just because you are ready to release the code doesn't mean the user is ready to accept it."
That played out for me today when I opened Thunderbird for Mac and it auto-installed the most recent release (68.4.1).
Immediately, I noticed all my e-mail accounts and e-mails within them were gone, gone, gone. Deep breaths....
So, I looked into this release and saw, "Thunderbird version 68.4.1 provides an automatic update from Thunderbird version 60." However, that was not the case for me and I suspect it may not be the case for others.
You must understand that I don't do "Inbox Zero". In fact, my inbox is my history for many things I do (along with the thousands of pictures on my phone). So, I was somewhat panicked.
However, I knew the e-mail files were there, just not being seen by the new version. Plus, I have redundant backups, so I knew I could get everything back. And...the beauty of the Mac is that you can just run the app with no install process like in Windows.
I managed to find the old version at
https://ftp.mozilla.org/pub/thunderbird/releases/
I downloaded version 60.9.1 (you will need to navigate through the sub-folders to get the right language version).
I opened it and instantly had access to all my e-mails.
The new version (68.4.1) looks great, but it was useless to me. I hope it works for me better in future releases. But for now, I have "auto update" turned off!
I hope this helps you!