No. BUT, I'm sorta' paranoid and anytime there is a MAJOR update of anything, I do backups. So, I suggest doing a backup of profile, not because of any problem I anticipate, but because it never hurts. here is the info in brief steps: '''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, has run at least once, 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 will prompt to overwrite an existing folder of same name. allow it # start thunderbird and all should be there