Close TB > in the 115 .18.0 profile folder, delete the compatibility.ini file > restart TB.

Regrettably, Ed, no better results. Interesting to find that compatibility.ini was in my original .default-release profile (Jan2025) and in the new .default-esr profile. I started fresh by deleting .thunderbird on the new PC, launched 115.18.0, closed TB, pasted my older PC .thunderbird contents into the new PC, deleted compatibility.ini (once just the new one and once both) and raunched TB. No difference in results, but shortly after launch 128.12.0esr was downloading and installing.

I should note that my older PC offers no way to upgrade 115.18.0 but 128.12.0 is offered as an additional installation. I wonder if both would coexist and if 128.12.0 would pickup the profile from 115.18.0...

was the copied profile created when thunderbird was running? If so, that is a common problem. The compatibility file should not be an issue for routine upgrades. I suggest carefully recreating the thunderbird profile copy and repeating the install of same release on new computer. Hold off on upgrading until all seems ok.

The process is this:

Exit Thunderbird on both computers - they must not be running - do this now and do not start them until all in finished.

On old Ubuntu 22.04 Cinnamon ".thunderbird" folder should be in your /home/username/ folder. Get a copy of .thunderbird folder

On new computer Ubuntu 24.04 Mate Uninstall Thunderbird program access /home/username/ folder is the 'username' folder the same/identical as on Cinnamon ? I'm assuming it is exacly the same - please tell if it's not. In username folder - delete the current .thunderbird folder Then paste in the copied .thunderbird folder into the /home/username/ folder thus replacing it.

Install Thunderbird 128.12.0 from https://www.thunderbird.net/en-US/thunderbird/all/

Make sure you select for Linux OS And choose channel 'Thunderbird Extended Support Release' (it auto selects the 'Release' version so reselect the ESR)

When you first run, it it should auto pick up the .thunderbird folder and your profile and auto update the compatibility.ini file.

As you are putting an older version 115.18.0 into a newer version 128.12.0 there should be no problem with 'compatibity.ini' file - this is usually a problem if you are attempting to do the opposite where a profile was using eg: 128.12.0 and then you downgrade to eg: 115.18.0

Toad-Hall, you may have identified the issue! In past computer replacement the username was not the same on both and the transfer of TB profile succeeded. In this case the 22.04 Cinnamon username is not identical to the 24.04 Mate username. My initial assessment is that I need to reinstall 24.04 to change the username folder and all app references. And, actually, this would likely solve a different issue as well so I'll proceed with the effort.

Regrettably, Toad-Hall, your insightful method returned the same results. To get my username folder named the same on 24.04 as on 22.04 I had to reinstall 24.04. Then I followed the method you detailed, installing TB by extracting the tarball to home/username/SW_Installs/TB folder and executed TB from there. When TB opened there was no remnant of my accounts and just an account setup screen. A new .default-esr profile folder was added to .thunderbird.

I took a "what do I have to lose" approach and, by guess and by golly, closed TB 128.12.0esr, copied selected folders and files from my original .default-release profile into the new .default-esr profile, replacing a significant number of files. When I launched TB I had all of my accounts shown, but the master PW and account PWs were lost. After entering the account PWs a quick look and check gives the appearance that I have transferred my 115.18 accounts to 128.12.0esr. More time using the new install is needed to determine how well settings, filters, etc. were transferred. Now that I know it worked I wish I had documented which folders & files I copied into the esr profiile...

The reason I mentioned 'username' is because the 'prefs.js' file would have had various preference settings pointing to home/username/.thunderbird/profile name folder, so if the computer username was different, then the 'prefs.js' file would have needed some editing to make sure any reference to username was correct. Prior to any editing of the 'prefs.js' file, Thunderbird must not be running and I would advise creating a copy of that 'pregfs.js' to be used as a backup just in case an error occurred.

re :master PW and account PWs were lost This may have been a security reason. Master Password (now called Primary Password) is usually used by people who both share a computer and both use the same username. So the Master password then acts as an addition protection against prying eyes as both people would be able to see each others profile details. If Primary Password is removed then all stored passwords would get removed unless Thunderbird was running and correct Primary Password was entered.

However, as you copied the contents of one profile into another - I'm not sure whether the necessary files were indeed copied over, or whether uou deleted all the contents of the new esr profile before you pasted in all the copied data. That might explain them not working.

The files that concern passwords and certificates are : cert9.db, key4.db, logins.json, pkcs11.txt

logins.json = Stores encrypted passwords, and requires key4.db and cert9.db to work. Replaces signons.sqlite, which had replaced signons.txt. pkcs11.txt = Security module database. cert8.db, key3.db, and secmod.db were replaced by cert9.db, key4.db, and pkcs11.txt.