Needed to revert to an earlier version of Mojave after recent disastrous security update from Apple on 27 September. 1. Wiped and restored SSD from TM backup, except for user files in /Users/Username/Thunderbird folder, which was backed up separately by Chronosync. 2. Restored /Users/Username/Thunderbird folder from CS backup. On starting TB, got error "Unable to load address book file history.mab" as per attached image. Have checked with Chronosync support and both history.mab file permissions and containing profile folder permissions seem to be correct. I had several years' worth of emails on this laptop. Because I use POP3, almost all sent items were on this laptop only, whereas at least I can if necessary retrieve the incoming mail from another desktop, though that would be exceedingly tedious. The global-messages-db.sqlite and various other files are present and sufficiently large to plausibly contain all my "lost" emails, but may of course also be corrupted, as it seems history.mab is. abook.mab was not present, but I copied it over from a newly created folder. Perhaps I was wrong to believe that TB application installation folder and TB user dependent including profiles folders are truly separable? One may have been backed up a day or two after the other. I did not update TB to my knowledge anyway in the time between those backups. Or maybe, as suggested by Chronosync support, some changes were being made to a TB user file while it was being backed up? This seems like such a basic bug or major limitation, that I would have thought would have been resolved a long time ago, as both TB and CS are relatively mature software.| Any help would be greatly appreciated. ''more info: https://support.mozilla.org/en-US/questions/1306714''