Comment 28 for bug 1244619

Just for the record, 2.6.1 works fine with 64 bits Thunderbird builds and also with those which are localized (ie., using a language other than English). I say this because is hard to find updated documents about this and the few I found seem to be pretty outdated (section "Extensions and themes"):

http://kb.mozillazine.org/64_bit_builds