See https://support.mozilla.org/en-US/questions/1359699

Thanks, Christ1, but in the question you referenced the user neglected to copy the thunderbird folder. That's not my problem. I copied the whole thunderbird folder from the Macbook Air to the iMac. I think the problem may be in the profiles.ini file. Profiles.ini on the source computer looks like this:

[Install8216C80C92C4E828] Default=Profiles/geiq1l61.default

[Install2E1C705BF359CCE5] Default=Profiles/geiq1l61.default Locked=1

[Profile1] Name=default-release IsRelative=1 Path=Profiles/79xrdgh9.default-release

[Profile0] Name=default IsRelative=1 Path=Profiles/geiq1l61.default Default=1

[General] StartWithLastProfile=1 Version=2

geiq1l61.default is the name of the correct profile. profiles.ini on the target computer looks like this:

[Install8216C80C92C4E828] Default=Profiles/geiq1l61.default

[Profile1] Name=default-release IsRelative=1 Path=Profiles/gtjw7lyd.default-release

[Profile0] Name=default IsRelative=1 Path=Profiles/geiq1l61.default Default=1

[Install2E1C705BF359CCE5] Default=Profiles/geiq1l61.default Locked=1

[General] StartWithLastProfile=1 Version=2

[Install59AB7BD93E662B32] Default=Profiles/gtjw7lyd.default-release Locked=1

So some things changed during the transfer. Are all those [Install...]s really necessary or correct? Should I copy just the profiles.ini from the source to the target? Or edit the target profiles.ini in some way?

Thanks, Ted

... in the question you referenced the user neglected to copy the thunderbird folder. That's not my problem. I copied the whole thunderbird folder from the Macbook Air to the iMac.

When copying the entire Thunderbird folder, the idea is to copy everything, including the profiles.ini file from the source computer. When the profiles.ini file is different on the destination computer, than possibly you did do something wrong.

I'm not a Mac user, so I'm not familiar with the folder location on a Mac. However, when you follow the instructions precisely it should work.

Unfortunately it doesn't. I've downloaded and installed the latest version of TB to my target computer. Then I followed the instructions in the FAQ. Didn't work. So next I deleted the Thunderbird folder from the Library folder on the target computer and again copied the Thunderbird folder from the Library folder of the source computer to replace it. I checked the contents of the profiles.ini file to see if they were the same on both computers. They were. I restarted TB on the target computer and again it tried to get me to set up a profile from scratch. I.e.it did not recognize the profile that was already there. I checked the contents of the profiles.ini file and saw that it had been changed - a new Installation and a new Profile had been added. So running TB91.3.2 causes changes in profiles.ini even if a valid, working profiles.ini is already there. Why is it doing this and what can I do to fix it?

Thanks, Ted

When you start Thunderbird on the target computer, what is the actual profile being used? Presumably it's not the geiq1l61.default one?

Check the first part of this article to try the existing profiles known to Thunderbird. https://thunderbirdtweaks.blogspot.com/2019/09/i-lost-my-profilemail-on-update-to.html

Does one have your missing data?

Thanks Christ1. We are making some progress. Yesterday I again copied the TB folder from the source to the target computer. When I started TB it didn't recognize the source profile, but created a new empty one and asked me to complete it (just like before). However, in looking at HELP|Troubleshooting info|profiles|about:profiles I saw that the source profile was registered, but not being used as the default. I clicked on the button to make the source profile the default and that worked. The source profile loaded and I was able to send/receive/read emails from all my accounts. Unfortunately it didn't last. Today when I start TB it again creates a new empty profile and asks me to complete setup. When I look in about:profiles I do not see the source profile registered. It is present in the profiles folder, but profiles.ini looks like this:

[Profile1] Name=default IsRelative=1 Path=Profiles/y3b4dfll.default Default=1

[Profile0] Name=default-release IsRelative=1 Path=Profiles/rrj827i1.default-release

[General] StartWithLastProfile=1 Version=2

[Install59AB7BD93E662B32] Default=Profiles/rrj827i1.default-release Locked=1

No sign of geiq1l61.default. It seems to have deleted the previous profiles.ini and replaced it with this new one. Why does it keep doing this?

Thanks, Ted

The 'profiles.ini' file seems to be showing more than one version of Thunderbird.

Question: Do you have exactly the same version of Thunderbird on both Macbook Air and iMac? If no, then make sure they are the same. Ideally, update the Macbook Air to latest version which is 91.4.0

Exit Thunderbird on Macbook Air then copy the ~/Library/Thunderbird folder.

On iMac - I'm assuming you have installed 91.4.0 Exit Thunderbird. Access the ~/Library and delete the default 'Thunderbird' folder Then paste the copied 'Thunderbird' folder into the Library

Start thunderbird.

I'd just reconnect the missing profile.

To recover the missing profile using the Profile Manager, follow these instructions:

1. Completely close Thunderbird, then start the Profile Manager. A "Choose User Profile" or "Select User Profile" dialog will open. https://support.mozilla.org/kb/using-multiple-profiles
2. Click on "Create Profile..." and, in the dialog that opens, enter a descriptive name for the profile you are recovering.
3. Click on the "Choose Folder..." button. A "Browse for Folder" dialog will open.
4. Select the profile folder that contains the user data you wish to recover and click OK.
5. Review the path shown in the "Create Profile Wizard" dialog to make sure it is correct, then click "Finish" (or "Done" on Mac OS) to create the new profile.
6. The new profile containing your recovered data will now appear in the Choose User Profile list.

Select the new profile and start Thunderbird to verify that your profile data was successfully recovered.

Once everything is working remove any orphan entries in your profiles.ini file.

Actually I was running version 91.3.2 on both computers, but I have now updated both to v 91.4. Let me copy the TB folder over again and then I'll try reconnecting the missing profile if necessary.

Switching both to v91.4 didn't help by itself. However, this time the source profile did appear in about:profiles and when I made it the default and then exited TB and then restarted TB it worked. Restarting TB from the about:profiles pane did not work. Anyway, thanks for all the help. It seems to be running OK now. But I guess somebody should update the FAQ or fix the program so that it behaves according to the FAQ to avoid further similar incidents.

Ted