>> I'd say that it's using a non-compatible fontconfig version, do you have
>> fontconfig installed from pkgsrc, and is thunderbird using it?

n40:~> pkg_info | grep fontconfig
fontconfig-2.2.96nb1 Library for configuring and customizing font access

n40:~> pkg_info | grep freetype
freetype2-2.1.9nb1  Font rendering engine and library API

Martti