Have been using the 104.9.0esr 64-bit release on Windows 11 for some time now (mostly for email, involving a number of email accounts) and have been generally satisfied... ...but discovered when I started looking into switching over to the 145 default release that I have a capital-P Problem. The first thing recommended on making that change is - sensibly - to back up one's Thunderbird profile. Only as far as I can tell, I don't *have* any such file anywhere on my system. [To answer the obvious question - yes, I've got "View" set in File Explorer such that it should be showing me hidden files.] I have drilled downward through all the USERS subdirectories on my C: drive. "Default" and "Public" have nothing at all (as one might expect). My personal subdirectory has a Mozilla directory under "Roaming", and both a Firefox and a Thunderbird directory therein, but the only things in the Thunderbird directory are an empty folder labeled "Crash Reports" and a tiny "desktop.ini" file. There is a "Mozilla Firefox" directory under Program Files, but nothing in that hierarchy looks applicable. There is a "Mozilla Maintenance Service" directory under "Program Files (x86)", but nothing there appears relevant. There is a "Mozilla [alpahnumeric hash]" subdirectory under "Program Data", but nothing there appears relevant. And in fact, I begin to think I have a bigger issue than I thought I did...because the more I poke at my C: drive, the less I'm seeing...to the extent that I'm not at all sure where the Thunderbird program itself (not to mention a quite large accumulation of associated email) is being kept. Which would be nice to know if one were attempting to back up one's mail before changing program versions....