This is how I've always done it (Windows). It preserves your whole existing setup. Copy TB files from the old PC - launch TB on the old PC - go to TB menu > Help > Troubleshooting Information - click the Application Basics > Profile Folder 'Open Folder' button - the profile folder will open - navigate three levels up to the AppData\Roaming folder - close TB - copy the AppData\Roaming\Thunderbird folder to a flash drive --- Install and launch TB on the new PC, then start setting up the new profile. Skip to the next section if you've already installed TB and created a profile. - on the 'Set Up Your Existing Email Address' screen, enter name and email address only - click the 'Configure manually' link - scroll down and click 'Cancel' - exit setup - close TB --- Paste the copied TB files to the new PC - open the AppData\Roaming folder like you did above - delete the Thunderbird folder, or copy it somewhere if you want to save it - replace it with the Thunderbird folder from the flash drive - launch TB