Comment 63 for bug 747197

See the target milestone. No one is working on this right now or will in the
immediate future. There is a work-in-progress patch here, and now that the
style system has been changed to also store non-absolute URIs things should be a
bit easier (issue 1 in comment 29 should not be present anymore). So someone
who cares about this bug needs to pick it up and make it work.

I'd say that a first cut could skip cursor and content and just do @import,
backgrounds, and -moz-binding...