You can get 31.8 here:

https://archive.mozilla.org/pub/thunderbird/releases/31.8.0/

but I would rather copy the local mail and address books from the old profile to the new computer that's running TB 115. That's easier than upgrading 31 to 115 by installing several intermediate versions. Local mail is stored in mbox files - large files with no extension, named after folders - in account subfolders of Mail and ImapMail, and Mail/Local Folders , in the profile. Copy them, renaming if necessary, to Mail/Local Folders in the new profile, with TB closed. Address books are .mab files in the old profile. Import them to the new one from Tools/Import.

Hi & thanks so much for the whip-fast reply!!  :-)

It turns out that Thunderbird changed how the address books were stored after 78.14.0. So i first have to upgrade from 31.8.0 to 78.14.0, then upgrade from 78.14.0 to 115. Am i understanding this correctly per this tech note?

https://support.mozilla.org/en-US/kb/upgrading-older-version-thunderbird

I DID successfully download & extract version 31.8.0 from the site you referenced in your prior reply, but there is no ./configure file in the extracted files to execute. :-(

Any suggestions?

Thanks very much!

If you can export the address books to LDIF format with 31, they can also be imported in 115.

For instructions on installing in Linux (which I've never done):

https://support.mozilla.org/en-US/kb/installing-thunderbird-linux

I DID successfully download & extract version 31.8.0 from the site you referenced in your prior reply, but there is no ./configure file in the extracted files to execute. :-(

There is no configure, make, building or installer or such. The tarball is basically a archive as you just untar it and then run the thunderbird-bin to use the Thunderbird email client is the basics. You may then want to make a launcher on desktop, panel or such instead of using the command line to start Thunderbird each time.

Aaah, thank you James!  :-))) Now this makes sense.

I'll only be using 31.8.0 one time, to transfer the data from my old computer running 31.8.0, to my new computer, w/ this temporary install of 31.8.0.

Then, to continue the upgrade process, should i download TB 78.14 in a seperate directory & extract it there, then copy the profile from the 31.8 0 directory to the 78.14 directory, then do the upgrade of 78.14 to 115?

Thanks again for your help James 😊🙏

You too sfhowes 🙏

I will follow up with how thing go

There is another method for exporting mail from 31 and importing to 115: install ImportExportTools on 31, export the mail to mbox files, then import them to 115 with ImportExportTools NG. This method is better when there's a complex folder structure.

If you try to upgrade 31 to 115 with all the intermediate versions, you run the risk of carrying forth a profile with many obsolete and possibly damaging files. Transferring just the (mail, contacts) data from 31 directly to 115 avoids these pitfalls.