Comment 14 for bug 468898

For Chinese (or CJK) users, Firefox's choice to use serif as the default font is also questionable. Not only because it is inconsistent to the default font style for desktop (i.e. sans-serif), but also the non-optimal rendering performance of the existing serif CJK fonts (Song/Ming styles). Most users don't care the font categories when browsing web pages, but prefer consistency and clarity for on-screen use.

Perhaps someone should file a bug to Firefox upstream directly.