I had a POP account configured in TB and working perfectly since years, and now I wanted to have an IMAP account for that email address instead, and remove the POP account, but of course I wanted to preserve the messages that were already in the Inbox and Sent folders of the POP account, by moving them into the new IMAP account. Now I know that I should have read https://support.mozilla.org/en-US/kb/switch-pop-imap-account , but instead this is how I damaged the local folder of my account: 1) I had this POP account configured in TB, and it had messages in its Inbox and Sent folders. 2) I created in TB a new account for the same email address, but IMAP. 3) I wanted the preexisting Inbox and Sent messages of the POP account to be available from my new IMAP account, so under Server Settings / Local Folder of the POP account I selected a newly created dummy folder, and in the IMAP account I selected the local folder that used to belong to the POP account. 4) Unfortunately this did not cause the IMAP account to show any of the messages from that local folder - (yeh, I have been reckless and asking for trouble, definitely). 5) I wanted to get access to those messages again, so I pointed the IMAP account to a new folder and the POP account back to its original local folder. But having been temporarily pointed by an IMAP account has apparently corrupted that local folder, because once it was back to being pointed by its original POP account, that POP account showed in the GUI an empty Inbox and no Sent folder. (Every time I have pointed an account to a folder, I have always let TB restart.) Now that local folder is still pointed by its original POP account, but now it shows no messages. Is there a way to get to those messages somehow ? I know they are there because if I go to that folder in the file system I can see that the "Inbox" file is big, and opening it with a text editor shows the messages I want, but unfortunately TB can no longer read those messages.