Filing this bug on finishing off / landing patch 8 in bug 735898, to remove the secondary content-order sort when we're sorting display-lists by z-index. For background, see bug 735898 comment 50 & beyond.
Actually, it looks like bug 748646 is already filed as a followup on this.
Actually, I shouldn't have duped this -- this bug isn't really a duplicate of bug 772690 -- it just depends on it. That bugs' patches are now landed (on m-i), so the content-order-sort in SortByZOrder can now land without causing orange. So, I'll land the SortByZOrder tweak in this bug. (simply using the changeset for part 8 from bug 735898, but with commit-message updated to point to this bug instead of that one)
Created attachment 644938 [details] [diff] [review] fix [r=dbaron granted in bug 735898 comment 47] Here's the patch (review already granted in bug 735898 comment 47)