Está coberto em este extenso FAQ no site da mozillazine.
Misread, você tem um novo perfil e quer copiar as coisas antigas? Mesmo documento, mas seção diferente, link específico .
Quais eventualmente vão para cá .
O que diz,
The simplest way to migrate your mail is to copy Mail and ImapMail (and their sub directories) to the top directory in the new profile, overwriting the existing ones. See Empty folders if it doesn't work.
However, the safest way is to use the ImportExportTools extension to import whatever folders you want to keep. When you run the menu command, it gives you the option of selecting a directory and having it find and select all of the folders in that directory and its subdirectories. See Importing folders for how to install and use that extension.