Just having switched to Thunderbird on OSX. The import facility does not seem to accept vcf files from the Address.app. I found a java implemenation that converts vcf to ldif [1].
A perl script [2] did work properly while moving vcf to csv, but it might work for you [2].
[1] http://big.faceless.org/misc/vcf2ldif.jar
[2] http://coollame.org/archives/000516.html
