Keeping your address book up to date helps to ensure you always have access to important contact information when you need it. If you're moving to a new computer, you need not leave your Thunderbird contacts behind. But Thunderbird has a dedicated import and export tool that enables you to transfer address book contacts from one computer to another easily.
Click the account containing the address book you want to transfer to a new computer. If you have multiple accounts set up for use, they will be listed on the left side of the main Thunderbird window. If you only have one account, you can skip this step because it is selected automatically.
Click the "Address Book" button to open the address book for the selected account. The Address Book button is located on the horizontal menu near the top of Thunderbird.
Select the address book you want to export in the left-hand column, click "Tools" on the main menu and select "Export" to load the Export Address Book dialogue box.
Enter an identifying name for the exported address book in the Save As field, verify that "LDIF" is selected on the Format drop-down menu and then click "Save" to export the address book.
Copy the exported file onto your new computer using a USB key, external hard drive or other portable media device. You can also email the file to your new computer as an attachment.
Open Thunderbird on your new computer, click "Address Book," select "Tools" and then choose "Import" to open the import wizard.
Click "Address Books | Next | Text file (LDIF, .tab, .csv, .txt) | Next" and then double-click the address book file you copied from your old computer. Click "Finish" to finish transferring your address book to your new computer.
If Thunderbird stops working or becomes corrupted on your computer you can still access its address books manually. Press “Ctrl-E” to load the File Explorer application in Windows 8.1 and enter “*.mab” in the Search field. Thunderbird saves address books with the MAB file extension. Your personal address book is the file called “abook.mab” and the collected address book is called “history.mab.”
To transfer these files onto your new computer manually, copy them onto a USB key or hard drive or email them to an account accessible on your new computer. Launch the File Explorer application and drag them into your Thunderbird profile folder.
To locate your Thunderbird profile folder, swipe your mouse to the upper-right corner of your Windows 8 screen and enter “%APPDATA%” without quotation marks in the Search field. Click “Roaming,” select “Thunderbird” and then choose “Profiles.”
You can also find your profile folder by navigating directly to the following address in File Explorer. C:\Users<Windows user name>\AppData\Roaming\Thunderbird\Profiles\