Restoring Thunderbird after Windows Reinstall

You want to put the mbox files in the Local Folders pseudo-account. Your Local Folders pseudo-account seems to be hidden.

1. Click on the three dots on the right of the "new message" button and uncheck "Hide local folders".
2. Install the ImportExporttoolsNG add-on.
3. Right click on the Local Folders account name in the folder pane.
4. Select ImportExportTools NG > Import mbox files > All mbox files from directory.

Thank you for responding. When I looked at that drop-down, "Hide local folders" was not checked. Please see updated attached image.

It seems that you do not have a Local Folders account. I just learned by creating a new profile without setting up an account that Thunderbird does not create the local folders account if no other account is set up. That surprised me.

So I suggest that you create a new profile and set up a dummy account. During the process, you will have to select "configure manually" and/or "advanced configuration" to prevent Thunderbird from trying to connect to the dummy account on a server. When you are done, you will have the dummy account and the local folders account. Then you can import your mbox files.

Then you may have to put Thunderbird in off-line mode so it does not try to connect to your dummy account all the time.

Create a new profile by "Help" (menu) > Troubleshooting information > about:profiles > Create new profile.

Then set the new profile as the default profile.

I have not encountered this situation before. Someone else may have better ideas. Nonetheless, this approach seems obvious to me.