Hello there Scholes. We have read your message we try to help you. Here you can go back into the newer and older version types. https://ftp.mozilla.org/pub/thunderbird/releases/ MBOX: – This type of MBOX file format is the “original” system mailbox format. MBOXO uses a particular constant string termed “???@???” in place of a sender’s email address. MBOXRD: – This type of an MBOX file is nothing but a variation of the MBOXO mailbox. MBOXCL: – UNIX “System V” mailboxes use the MBOXCL file extension. MBOXCL2: – This sort of MBOX file extension bears similarities with the MBOXCL format. You can find your folder and emails back in the profile map. http://kb.mozillazine.org/Importing_folders#Find_your_old_profile Your agenda has to be configured again. Greetings Firefox Volunteer.