Rated 5 out of 5 stars

Since the account has been locked up with previous developer, I can't upload the updated version. Thus, this is an unofficial version compatible with firefox 3.6.x.
Just copy and paste it.
http://www.magotemple.com/BLOGS/Blog-Posts/koreanspellingandgrammarcheckerforfirefox36x

This review is for a previous version of the add-on (0.3.5).