The easiest way to do this is to run Thunderbird, let it create a new profile, close and exit Thunderbird, then overwrite that new profile with your old one.

https://support.mozilla.org/en-US/kb/profiles-tb

Help|Troubleshooting Information provides an easy way to open the profile folder in your file manager.

As you're moving between different operating systems, you may need to edit the profiles.ini file, especially if it refers to file or pathnames. C:\ is unlikely to make any sense to Ubuntu, or any other Linux based system.

Note that two add-ons in particular cannot be transferred, as, at present, they need to be compatible with the version of Thunderbird compiled for the particular platform in use. These are Lightning and Enigmail.

Where in UBUNTU LINUX is the profile and message data files stored? Not that the old TB is on a Windoze installation and the NEW TB is on Ubuntu Linux.

The link I gave you in my first post tells you that.

Zenos said

The link I gave you in my first post tells you that.

It refers only to Windows, not to Linux. The Winows data file I have already copied and placed in a folder waiting for someone knowledgable about Linux can reveal the TB location into which the data will be transferred.

Try opening the link in your Ubuntu. The website detects the OS in use and adapts the information accordingly.

Or run Thunderbird on Ubuntu and use Help|Troubleshooting Information to open the profile in your file manager.

Please take care to close Thunderbird before attempting any modifications to the profile folders. Else it will write back to update its profile, on closing, and undo your work.

For the record, on LMDE, it's

~/.thunderbird/

YMMV. But this location isn't mandatory. The only file that absolutely must be there is profiles.ini, and it can refer to any reasonable location. I guess profiles.ini could be a symlink to a real file located elsewhere, but I haven't tried that for myself.