It never hurts to do a backup: so I include steps for backup and, if necessary, restore. Since you're doing an upgrade of windows, and not a new computer, you could backup the thunderbird folder to another location on hard drive, if desired. On your question, there shouldn't be a problem, but I always do backups. '''BACKUP''' # ensure thunderbird is not running # enter %appdata% in search window on task bar and press Enter key # this should open windows file explorer in Appdata\roaming folder # highlight the Thunderbird folder and copy to external media '''RESTORE''' # ensure thunderbird is installed and NOT running # enter %appdata% in search window on task bar and press Enter key # you should be in Appdata\roaming folder , copy&paste the exported Thunderbird folder there. This may prompt to overwrite an existing folder of same name. allow it # start thunderbird and all should be there