I'm trying to restore my Thunderbird mailboxes from my old (essentially dead) computer's backup to a new computer. My first attempt failed. I need to understand what went wrong and how to correct it. I installed Thunderbird on the new computer and used Profile Manager to create a profile in the location where I want to keep it (in the Documents folder, to simplify backup). Then I found the place where the mailboxes were kept and copied my old mailboxes there from the backup. Then I started Thunderbird. Instead of displaying my old Inbox and a list of mailboxes, it displayed a screen that prompted me to define my email account. OK, that's fair; if the account information wasn't in the files I copied, Thunderbird would have to do that. After I defined the accounts (there are three), I quit and restarted Thunderbird, and it displayed my Inbox and mailboxes. But not quite as I expected. I expected to see the mail that was on the old computer when I last backed it up. Then I planned to download mail to get everything that came in after that. Instead I found that Thunderbird had erased everything I copied over, then downloaded the new mail without me asking it to. Now what? The new mail is still on the server, so I can repeat the whole process if I have to. First, though, I need to understand what went wrong.