Uncertain what you are asking I do? I believe I confirmed the active profile is on the C: %APPDATA% path on the source machine, and confirmed this is what is copied to the target machine? What, please, have I missed in your requests for information?

I have only skimmed this for recent changes. However at the risk of duplicating things I will just have my say. Sorry in advance.

These are the steps I take without success: On the source machine I locate the profiles with [Windows] Run %APPDATA%\Thunderbird\Profiles and File Explorer opens to that location.

Use the Troubleshooting information on the help menu to to open your profile folder in the windows file explorer.

Copy the Thunderbird folder and all subfolders to a USB drive.

copy the contents of the Profile folder and the subfolders to your USB drive.

On the target machine, install Thunderbird, and run it once. Ignore the prompts for an email address and open Help - More Troubleshooting Information - Open Profile Folder and confirm Thunderbird created a new profile.

Now close Thunderbird.

Go up three levels to \Roaming\ and confirm the subdirectories Thunderbird Profiles Close Thunderbird.

Insert USB drive on the source machine and copy the source Thunderbird folder to the new %APPDATA%\Thunderbird\Profiles and overwrite the newly created Thunderbird folder from the \Roaming\ folder level. When prompted, replace all files with the same filename. Start Thunderbird on the source machine. No email, no addresses.

Now with the profile folder open and Thunderbird not running copy the contents of the profile folder into the new profile you opened from the troubleshooting information.

You should be plagued with replace error in file manager, but at least you know you are replacing the new profile data with the old.

Thunderbird's profile per install is a fickle beast and while the developers are having some sort of love affair with the concept it is a regular pain for those that are actually trying to achieve simple things like move to a new device.

By allowing the program to decide what the profile is called and simply replacing the folder contents on that profile it has created for the new install, you bypass profile per install and all of the foibles on paths, executable names and the whole mess 32 Vs 64 bit versions cause through it.

I have the same problem. I've been moving files between three computers without incident for maybe 10 years now. I"ve used various locations on different machines, so that the profile folder is easier to address, and most of the time in virtual (encrypted) file systems. My files are larger than 2GB. Never a problem, but that stopped with release 100. I"m currently on 115.2.3 on two computers and have the following observations:

1. Copying from a computer with release 100+ to one with a lower release just won't work.

2. Copying to an SD card then to a second computer now gets the Account Setup window without recognition of many files. There is one exception to this. Copying worked one time in one direction. It has never worked in the other.

3. I can copy the files back and forth to different locations on the same computer, setting up different profiles and it seems to work pretty well, until I copy them to a virtual disk (which is located in an encrypted file) on the same computer, and I get the Account Setup window, like Gwendolyn.

4. I have looked at the instructions in this thread and followed them precisely, with no success in getting files moved.

My conclusion is that something changed in release 100, and there is something machine-specific that needs fixing so the files can move properly.

OK, a bit more troubleshooting.

I copied the profile folder to various places on its existing computer and it works just fine, unless I copy it to a virtual disk, in which case I get the Account Setup screen.

If I copy the profile folder to an SD card, and then either point to the SD drive directly or copy it back to the computer -- Account Setup.

I've tried to create a new profile folder (gives Account Setup), then wipe the contents and replace them with the contents of an original folder -- Account Setup.

When I do the copies, I always get the pref.js file flagged, so I tell the copy program to skip it. I've never had a problem with doing that in the past, and it isn't a problem now when the copy is from one location to another on the same computer.

Seems to me something goes wrong with the copy, but I can't figure out what it is. All the troubleshooting information and profile data seem right, so the particular instance is finding the right folder, but apparently ignoring all the data.

Any ideas what to do next?

I have the same problem. I've been moving files between three computers without incident for maybe 10 years now.

And therefore are in the most likely to fail group of users as you do not account for the profile per install. https://support.mozilla.org/en-US/kb/dedicated-profile-thunderbird-installation

I"ve used various locations on different machines, so that the profile folder is easier to address, and most of the time in virtual (encrypted) file systems. My files are larger than 2GB. Never a problem, but that stopped with release 100. I"m currently on 115.2.3 on two computers and have the following observations: 1. Copying from a computer with release 100+ to one with a lower release just won't work.

Read the article on profile per install. It is not some sort of bug or accident.

2. Copying to an SD card then to a second computer now gets the Account Setup window without recognition of many files. There is one exception to this. Copying worked one time in one direction. It has never worked in the other.

Again refer to the same article.

3. I can copy the files back and forth to different locations on the same computer, setting up different profiles and it seems to work pretty well, until I copy them to a virtual disk (which is located in an encrypted file) on the same computer, and I get the Account Setup window, like Gwendolyn. 4. I have looked at the instructions in this thread and followed them precisely, with no success in getting files moved. My conclusion is that something changed in release 100, and there is something machine-specific that needs fixing so the files can move properly.

Nope, just move the contents of the profile folder to the newly created profile. The old ideas of copying the profile folder or the profiles folder or even the Thunderbird folder with the profiles.ini file in it is no longer going to work.

If you actually require support after reading the relevant support documentation then I suggest you open your own topic. Clearly this topic has a different issue to what you are on about as it does not solve your problem.