Rated 4 out of 5 stars

In version TB 52.3.0 (32-bit) and CardBook 21.8 is still a problem with importing vCard - it is not possible to import a .vcf file to any folder in CardBook:

1st way: in CB - right mouse on folder - import from file - select file ...and nothing happened;

2nd way: in any explorer outside - open in a program - choose program - Thunderbird ....and contact will be import to DEFAULT folder of TB (default address book), not into the CardBook. And is impossible to copy it to CB.

edit:
- tried to switch version of vCard between 3.0 and 4.0 in settings - nothing happened;
edit 2:
- tried to check box "unique source for contacts" in settings of CB - nothing;
- tried to import .vcf file exported by CardBook - OK, imported without errors;
- tried to import .vcf file generated by another source, e.g. Android 6.0.1 - nothing imported.

result:
- .vcf files version 2.1 (e.g. generated by Android 6) are not supported by CardBook.
- Thunderbird can import .vcf version 2.1 into address book, but export only version 2.1.
- in CB only version 3.0 and 4.0 are supported.

This review is for a previous version of the add-on (21.8). 

may you send me your vcf file : cardbook.thunderbird @ gmail.com (otherwise check the CardBook log)