I think this addon does what you want. https://services.addons.thunderbird.net/en-us/thunderbird/addon/outlook-address-book-enabler/ If not, please provide more information. As an aside, thunderbird does support importing csv and LDIF and vcard formats.

Hej David. Tak for svaret. Thunderbird er nyt for mig og aner ikke hvad jeg gør med tilføjelsen. Har fundet et sted hvor der er tilføjelser til Thunderbird, og tilføjet det du sendte.

Her fra er jeg tabt og ved ikke hvad jeg så skal gøre. 

Hvad med import af CSV-, LDIF- og vcard-formater. når jeg har importeret fra Outlook ? Da jeg i outlook adresse kartoteket har en gruppe med kontakter troede jeg den blev overført sammen med alle de enkelte kontakter.

The addon added an extra support feature to Thunderbird. The instructions on using the addon are at

https://services.addons.thunderbird.net/en-us/thunderbird/addon/outlook-address-book-enabler/   From the addresbook pane, you will find the ability add an LDAP server by clicking the icon to the left of the NEW CONTACT icon and then follow instructions as in the URL i included. I cannot speak to Outlook group ids. All I can suggest is to review content of exported csv or ldif files you created from Outlook. If you prefer to import a csv or ldif file, it can be complex as the fields don't readily line up. To be successful in this here is my suggestion:

1. create at least one email address in the thunderbird address book
2. then, highlight the addressbook and click the three dots to the right of the addressbook name and export the file
3. you mow have a template
4. open the file in a spreadsheet program to view the top row. this tells you the layout of the thunderbird addressbook
5. now, open the exported file from Outlook in the spreadsheet program and adjust the columns to match the thunderbird layout
6. now, click tools>import>import from a file and follow the menus for addressbooks