This is how I've always done it (Windows). It preserves your whole existing setup. Copy the TB files from the old PC: - launch Thunderbird on the old PC - go to Thunderbird menu > Help > Troubleshooting Information - click the Application Basics > Profile Folder 'Open Folder' button - the profile folder will open; navigate three levels up to the Roaming folder - close TB, then copy the Thunderbird folder to a flash drive --- Paste the TB files to the new PC: - go to the new PC's Roaming folder as instructed above and delete the Thunderbird folder - paste the Thunderbird folder from the flash drive to the new PC - launch Thunderbird