it is more likely caused by the use of snap installers in Ubuntu and therefore mint.

why are you not using a current release. 128 is also out of support.

Hello Matt, I don't know why I am not using a "current release". The Thunderbird on my Mint machine came with the Thunderbird that I have. I want desperately to solve my current problem first. I can look at changing to a newer release later if there is a case for it. I do not understand the reference to "snap installers".

I'd be inclined to first update win7 to 128, then attempt the move to linux with version 128.

Install and start 128 on the linux system, let it create a directory, then copy your windows profile directory into that. It should create xxxx.default-release directory. (Profiles named xxxxx.default in not used in normal practice, so I'd avoid that.)

Then describe your problem, if any.

Thank you Wayne, Unfortunately, Thunderbird regards Win7 as such an outdated operating system, that it aborts any attempt to upgrade on that platform. Apart from that detail, I have tried what you suggest. I plan to list the contents of the xxxxx.profile-default folder on the two machines to see if they at least have content items with the same names. Do you know where I could get Thunderbird 115.18.0 to install on the Mint machine?

Do you know where I could get Thunderbird 115.18.0 to install on the Mint machine?

https://ftp.mozilla.org/pub/thunderbird/releases/115.18.0/

Select the appropriate linux option, then select the desired language, finally click on the 'thunderbird-115.18.0.tar.bz2' to get a download.

Note: I recall when moving from Windows to Linux it helped to delete the 'pkcs11.txt' file in the profile. If profile in Linux used a version more recent than 115.18.0 then delete the 'compatibility.ini' file.

Basically Exit Thunderbird on both computers. Copy all the contents of the profile name folder on Win7 On Linux - locate the default profile, remove all contents and then paste in the copied contents then delete 'pkcs11.txt' file and 'compatibility.ini' file. Start Thunderbird.

Thank you for your attention to my matter Toad Hall, Unfortunately, the url you provided does not seem to provide a place to: "Select the appropriate linux option, then select the desired language, finally click on the 'thunderbird-115.18.0.tar.bz2' to get a download." As I have explored around, it has become clear that I have to learn more about downloading software in Linux before I tackle that. As to your suggestion that I can make the transferred profile work by deleting pkcs11.txt and compatibility.ini, I did some research on the dichotomy between the ******.profile and the ******.profile-default folders. Some of the advice on the web contradicts other advice on this point. I may not have "the" picture, but I now have a clear idea of "a" picture here. I have tried following your instructions with the transfer of various combinations of these folders, but, unfortunately, none of them work. All lead to that dreaded octopus page. I will go back to trying to learn enough to install 115.18.0 on the Mint machine to see if I can transfer the profile when both machines have the same version of Thunderbird. Thanks again.