I tried this but when I choose address book, text file , than next I come to screen that wants me to enter filename, not ok and finish when done. System is using Windows 8 i that would make a difference
1.) Find on your computer (main computer in my case) the file: abook.mab, which is Thunderbird's "Personal Address book"
2.) Copy the file - abook.mab -from the pen drive onto the second computer, in my case my laptop. (In "Everything" I can copy the path and file it easily, such as L:\ThunderbirdPortable\Data\profile.)
3.) Rename the current abook.mab on the second computer - my laptop, for example - to: abookORIGINAL.mab just in case of trouble.
4.) Paste the imported updated address book (abook.mab) into that path.
In this way you now have the "Personal Address Book" of Thunderbird duplicated into the second computer- my laptop in this case.
(P.S. I leave abookORIGINAL.mab on the second computer in case I have an address that I forget to incorporate into the current abook.mab that is on my main computer.)