Comment 76 for bug 29622

This problem currently has little chances of getting fixed, since the printing subsystem in Mozilla Core used by Firefox is practically unmaintained.

See:

https://bugzilla.mozilla.org/show_bug.cgi?id=284925
https://bugzilla.mozilla.org/show_bug.cgi?id=130075

I think the developer who is able to fix this is Roland Mainz (http://www.nrubsig.org/people/gisburn/) who quit working on Mozilla a couple of years ago. Maybe Canonical could hire him for the task of improving Mozilla Firefox's printing and its CUPS integration?