The profile folder location is defined here:

http://kb.mozillazine.org/Profile_folder_-_Thunderbird#Mac_OS_X

so the Thunderbird folder is in ~/Library/

When you copy a profile between OS X and Windows, delete the pkcs11.txt file on the target computer, after the copy, to avoid having the stored passwords not read. The file is automatically recreated when TB restarts.

Follow these directions for installing TB on OS X to achieve a correct setup.

Thank you, sfhowes. I'm still stumped :-(

I *think* TB installed correctly, as Thunderbird.app is securely in the Applications folder of HD. I have rebooted, and it remains there, and responds correctly, i.e. shows my email account and checks for incoming.

But I still can't find a Thunderbird folder anywhere ... or at least anywhere I've looked.

There is an HD/Library, but no TB. There is a HD/System/Library but no TB.

HD/Users/myusername/ shows no Library or TB, only the usual Desktop, Downloads, Documents, etc.

Question: like Windows, is there a "hide system files" preference, or anything that might be hiding the myusername/Library/Thunderbird folder I'm looking for?

Sorry for my ignorance. I aced the A+ Mac module in 1995, but now feel like a nitwit.

Cheers! CJ

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Launch TB, then Help/Troubleshooting, Profile Folder, Show in Finder. That will open the profile folder in Finder, so you should see the Thunderbird folder by going up one level to Profiles and up one more to Thunderbird. Close TB before making any changes to the profile.

https://techbland.com/3-ways-to-show-all-hidden-files-on-macos-big-sur/