I suggest you start over to reduce problems: here is the info in brief steps: # ensure thunderbird is not running on old windows machine # 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 # ensure thunderbird is installed on second computer 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 By using windows file explorer, you get 100% of the profile, including stored passwords. This may not work for some accounts, but does for many.