My suggestion is to create an entry in thunderbird addressbook and then export as vcard and compare layouts of that with Mailbird's.

I created 1 vCard in Thunderbird exported it to my desktop and imported back into Thunderbird and it looks fine.

When I export a address book from Mailbird to the desktop as vCard and look at them there, they look ok. When I import the same vCard address book that looked ok on the desktop, into Thunderbird of the 58 cards only 7 have any information in them. The other 51 cards are blank. When I then export the 58 cards from Thunderbird back to my desktop and look at them I now have 51 blank cards and 7 with information on them.

When I look at the imported vCard address book in Thunderbird the blank cards are always at the top of the list and the ones that have information on them are at the bottom.

Of the other vCard address books that I imported only a few of the cards have any information in them as well. The number of cards with information on them is different but they are always at the bottom.

I admit to not knowing vcard well, but I feel comfortable with csv. If you do a google search for 'vcf to csv' there are several sites that will convert for you. Then, lrepeat the thunderbird extract of a csv file, load into a spreasheet program and also the converted vcf file and compare the top row. Readjust the top row of the converted vcf-to-csv to mirror the thunderbird template and you will be successful.

When I used an online converter and saved the vcard file as csv I was still unable to create a address book. Using the same online converter to save the vcard as ldif I was able to create a address book. I'm not sure why, but I have a usable address book so I'm happy. Thanks!