It may help to know exactly how you copied them.

Thanks David for your response. I exported a Personal address book and saved it as comma separated. I then imported this saved file into a newly downloaded Thunderbird. But I don't see any addresses. However, Total contacts are shown as over 400. When I later looked at what I saved to import, it was an empty spreadsheet. Now it seems that I have to delete those 400 invisible contacts.

If this is a 100% transfer from one addressbook to another, such as when setting up another PC, the BEST (and easiest) way is to transfer the profile, as that includes all accounts, all settings, and all addressbooks. But you're past that. To transfer JUST an addressbook, do this: - click tools>import>import from a file, and follow the addressbook links to the one allowing import from sqlite files, and then select the abook.sqlite file from your old profile. and then repeat, selecting the history.sqlite file. Now, if the old profile is gone, then you work with the csv that you exported. to do that, create one address manually in the addressbook, and then export it from thunderbird. open in a spreadsheet program and note the top row. That shows how thunderbird organizes the addressbook. Now, open your exported csv into a spreadsheet program and adjust the columns to match the one from thunderbird. once you have match, you can import the csv and it should work fine.