I had a fairly bad experience using China Southern's website trying to select the seat for an existing ticket, even with Chrome, Safari, and Firefox on an OSX desktop. (Trying on a Sunday afternoon Sydney time on 7 August 2016). At least it was in English, though. Is the website optimised for a particular browser, such as Internet Explorer?
Above: the result of trying to view online services for existing tickets.
Above: the result of trying to view some sort of information about existing tickets.