Export the mailbax from Netscape, must have a .mbx (lowercase).
Copy the exported mailbox to the Pegasus maildir, must be done one at a time
Open Pegasus, the folders will be added to the folder list.
Create a new folder, using Pegasus 2.x format
Select all emails from the Thunderbird folder and move to the newly created Pegasus folder.
Must be repeated as required for the balance of the mail folders. I was able to move just under 100 .mbx files this way.
Note: Pegasus will only see the new files (mailbox.mbx) on startup.