See these topics:

https://support.mozilla.org/en-US/questions/1247226

https://support.mozilla.org/en-US/questions/1202963

If you just use an old version of TB to import all Outlook mail, it will be placed in Local Folders, but using MailStore as an intermediary should allow you to select specific folders.

Thank you for your speedy reply. I have now downloaded and installed MailStore Home. Are you saying that I need to use an old version of TB to use MailStore to get my folder? If so, can I install the old TB version on the same computer that I am running TB version 78.2.2? John

If you just use MailStore to import from Outlook and export to TB, there's no need to use an older version of TB. TB 17 is only for importing directly from Outlook.

Some users have found that MailStore will copy the Outlook mail into TB, but if not, exporting from MS in mbox format produces a file that can be imported to TB by opening the profile folder (Help/Troubleshooting, Profile Folder, Open Folder), closing TB, and copying the mbox file into Mail\Local Folders of the profile.

I think that I am getting closer, but am not sure how to export the folder (in MS) to mbox format. I have a choice of E-Mail servers (Exchange Mailbox, Gmail, IMAP Mailbox), then a choice of E-mail Clients (Microsoft Outlook, Mozilla Thunderbirdd, Mozilla SeaMonkey) and a choice of E-mail Files (Directory (File System, Microsoft Outlook PST File). I selected Mozilla Thunderbird as the email client, then in a window called Export to Mozilla Thunderbird there was a folder called Outlook myemailaddress. Within that was the folder which I wish to bring into Thunderbird from Outlook. I clicked on that folder then clicked Next. I selected default as the profile name and checked Retain folder structure, then clicked Next. I got a window saying that "MS has created a new profile "Mozillla Thunderbird default. Double click to start archiving." I did that and got a message that the process completed successfully. I don't understand how to now get that into Thunderbird.

After the step 'MS has created a new profile...', launch TB and see if there is a new folder under Local Folders with the Outlook mail. If not, Help/Troubleshooting, Profile Folder, click Open Folder to open the profile folder, close TB, go up one level in File Explorer to the Profiles folder. Is there a new profile named 'Mozilla Thunderbird default'?

https://help.mailstore.com/en/home/Exporting_Email

I really appreciate your patience with me on this. In my Local Folders in TB I have a folder called MailStore Export. It has a sub-folder called Outlook myemailaddress.ca. That has a subfolder called Misc, which is the correct name for the folder that I am trying to get from Outlook, but this Misc folder is empty. When I click Open Folder in the Profile Folder of Trouble Shooting, close TB and go up one level there are two profiles, both old, but no new one. John

I really appreciate your patience with me on this. In my Local Folders in TB I have a folder called MailStore Export. It has a sub-folder called Outlook myemailaddress.ca. That has a subfolder called Misc, which is the correct name for the folder that I am trying to get from Outlook, but this Misc folder is empty. When I click Open Folder in the Profile Folder of Trouble Shooting, close TB and go up one level there are two profiles, both old, but no new one.

OK, so when they say 'new profile' they don't mean a TB profile, but a location in Local Folders. No idea why the Misc folder is empty. Perhaps try exporting with the Directory (File System) option, which should create eml files or an mbox file. Importing mbox is explained above, and with eml files you can drag them from File Explorer and drop them on the Misc folder icon under Local Folders in the TB interface.

Exporting with the Directory (File System) option worked. In the empty Misc. folder I recreated the folders that were missing, then used File Explorer to drag and drop the messages into those newly created folders. I am so happy with this. Thank you very much for your great answers. You have saved me a huge amount of bother and avoided a dispute over missing receipts with the tax man. John