Click on 'Address Book' Select the address book you want to save Right-click the address book name; choose Export Choose where you want to save the exported file. (Do not choose a folder in a Thunderbird folder.) Save as type: Comma Separated csv. Give the file a name. Then when you have the new installation finished, Select the address book you want to restore the contacts to. Right-click and choose 'Import' Navigate to the file you saved earlier. Select it. (Use the '''Continue''' button as you go through these steps.)