Open the Time Machine disk and navigate through the backups to the various instances of your user home folder and see if the "Library" folder is listed there and it should contain the backup 'Thunderbird' folder.

The default location for Thunderbird profile is: Hard Disk/Users/yourlogin/ Library/Thunderbird

Exit Thunderbird if it is running. Remove the default 'Thunderbird' folder from current 'Library' and copy paste the 'Time Machine' backup copy of 'Thunderbird' into 'Library'. Start Thunderbird.

Thank you, Toad-Hall, but this did not work. I followed these instructions explicitly; when I tried to reopen TB, it just kept hanging up and freezing my system, so I had to trash everything and restore TB. Of course, this meant that I lost everything and had to start from square one, beginning with adding email accounts, etc.

I know how to use Time Machine. The problem is that I do not know what I can do to possibly restore the settings, preferences, and folders I had before the crash caused by the upgrade. I think the solution has got to be more refined than simply deleting and copying everything. Wouldn't I be looking for the location of TB preferences and trying to restore that? Wouldn't I go through Library/Preferences to find that folder or folders?

Can anyone help me with this?

Probably https://thunderbirdtweaks.blogspot.com/2019/09/i-lost-my-profilemail-on-update-to.html All based around https://support.mozilla.org/en-US/kb/dedicated-profile-thunderbird-installation

Thank you, Matt. After reading through the first link, it did not account anywhere for having to go back to try to bring back a profile from a previous version of TB. But I tried an experiment—I copied and pasted the profile folder, through Time Machine, from a date before the upgrade and crash. I pasted it into my current TB profiles folder. When I restarted TB and went to about:profiles, though, this folder did not show up.

My non-expert assumption is that that older folder is the one I want to use (doesn't that contain all of the preferences and settings I want back?), but is it somehow incompatible with TB 78.7.1? I now don't remember the last old version number, but I tend to keep software up to date, and the upgrade/crash happened around Dec. 15 of last year.

My advice was to copy the 'Thunderbird' folder from Time Machine as it contained all the important stuff in the 'profiles,ini' file and paste into 'Library'. But you say you did not copy paste that Thunderbird folder instead you copy pasted the 'tloq09f4.default' folder into 'Profiles' folder, it does not auto update the 'profiles.ini' file, so basically Thunderbird has no knowledge about it.

You need to create a new profile and point it to that old profile, so the 'profiles.ini' file gets updated. Via Thunderbrd: Help > Troubleshooting Information click on 'about:profiles' Click on 'Create a new Profile' Give it a name eg: Default Original' click on 'Choose folder' and locate that 'tloq09f4.default' folder, click on Open click on 'Finish'

Then you should be able to choose the default profile and launch it.

Aditional info: https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-thunderbird-profiles#w_creating-a-profile

Toad-Hall: I DID indeed follow your original instructions to the letter. A few times. Your original instructions did NOT contain the information in your second paragraph above. When I tried to restart TB, it looked like my old version, and it hung, unresponsive, with the spinning beach ball of death.

I went back to scratch again, following your above instructions TO THE LETTER, and got the same result as before—hanging, unresponsive; I couldn't even get to the part about creating a new profile, which is why I tried the experiment I described above.

So I'm still stuck and can't retrieve my old folders, tags, prefs, etc. The image shows how TB looks when it opens and hangs. It looks like it has correctly retrieved email and is up-to-date, but it's frozen.

UPDATE: Deleting the TB app, downloading from scratch, and pointing about:profiles to the restored file WORKS!!!! Got back my folders, custom tags, along with the new default dark theme. Looks great!!

BUT—it only works fine until I quit.?!!!

When I try to reopen it, once again it hangs, looks like the old (light theme) version (see screenshot above) and never works and I have to force quit. So, if I go through the ENTIRE EXERCISE again, starting from scratch, and then never, ever quit after finally restoring everything, I'll be fine. But, of course, that doesn't solve the underlying problem.

So—what is the underlying problem here?

Are you actually installing the DMG or just running it? I have seen issues where folk just run the DMG as nothing saves between sessions because the changes are stored in the TMP folder and deleted by the OS.

It is one of the conveniences of MAC operating systems that really catches folks out at times.

AS per Matt's excellent advice: https://support.mozilla.org/en-US/kb/installing-thunderbird-on-mac Common Problems If you fail to install Thunderbird to the Mac applications, every time Thunderbird starts it will not have remembered your previous session settings - it will ask you to create email accounts, or otherwise indicate that it has no data. You must drag the Thunderbird dmg file/icon to the Mac Applications folder.

I always install the app on my desktop. In all of my attempts, I never started it from the DMG file.When I try to restart it, it isn't asking me to create accounts; it opens up looking like the OLD version of TB...and hangs.

Interesting possible clue? When the old version opens and hangs, look at the date, circled in the second image. Something screwy about the calendar it's using. It's always like that, with the correct date and year but the wrong DAY—today is obviously NOT Sunday. ??!!

Is there something I could search for in the prefs.js file? Or the problem report created when I have to force quit? Some different way I could try starting it up?