Last modified: 2013-05-29 18:03:10 UTC
Firefox applies a Korean font to elements with lang="koi". This is the Komi-Permyak language, which has nothing to do with Korean. This is an upstream bug.
Reported in Mozilla's Bugzilla: https://bugzilla.mozilla.org/show_bug.cgi?id=793881 Interestingly, this bug is somewhat similar to Bug 36264.
Can't reproduce anymore. Probably fixed upstream.