I'm actually slightly confused as to why Mike has provided a guide telling people how to modify core XenForo files because most people don't actually need the fixes. You go to any XenForo website, use Facebook integration and it will work fine in any browser on any OS.
You go to Mike's site specifically it won't work for very specific reasons.
I'm not saying things aren't out of date, obviously they are. But in this particular situation it is not a widespread issue or cause for concern. It's certainly not the case that you can describe XenForo as "falling apart" over this one thing.