In case this is helpful ... I lost all my Thunderbird contacts when my old computer failed so I wanted to import contacts from my Android phone. I exported all my phone contacts to a .vcf file and then tried to import that file into Thunderbird. It took a while to read about 1000 contacts and when it was done there were no contacts in my address book. Interestingly, when I exported that seemingly empty address book from Thunderbird as a .csv file it was fully populated. I read that file into Excel and deleted a bunch of empty rows and rows with garbage in them. Then I read the edited .csv file back into Thunderbird with success! This took me several hours to accomplish with much trial and error.