I found a article of mozilla event in Japan at May 31 2008.
Report: Incoming Firefox 3 is fastest! - mozilla party jp 9.0
http://journal.mycom.co.jp/articles/2008/06/01/mozillapartyjp9/index.html
Mozilla Japan says Gecko 1.9 uses ATSUI (Apple Type Services for Unicode Imaging). Ha????? Although Gecko 1.9 uses Cario 1.6.4 (stabled version) w/ some patches, Cairo 1.6 uses CoreText (CGFont) instead of ATSUI. So Gecko 1.9 doesn't use ATSUI. I cannot make sense why they explain invalid information for graphics backend... You know, ATSUI API set is from Carbon, and doesn't support on 64bit Mac OS X.
Also, as long as I checked cairo mailing list, Vladimir posted the following mail at March 17 2008.
Here's a patch that renames the current ATSUI font backend to a Quartz font backend, in preparation for eventually dropping the ATSUI dependancy internally and using CGFont directly. This patch makes --enable-quartz give you both quartz surface and quartz font support; otherwise, I would've needed to use "cairo-quartz-font.h", breaking the usual pattern. I also can't think of a reason to compile with just one of those -- even if you only use one or the other, it won't hurt to have them both available (since they have the exact same dependencies).
Vladimir is one of mozilla.com members...