My problem is, listed in the first link. Something caused thunar to get kicked, it got somehow replaced with nautilus. It's not just an error, but it's not 'good' either. I mean, the other I just boot my computer and you literally see nautilus hijacking my desktop. Also, every window with files is controlled by nautilus. After a while, I encountered a more severe problem. The trashcan, I have to remove everything manually (so that is settled). I can find my way around this new way. But it's not good.
Any suggestions what could have caused this?
Can it be reversed? I like nautilus, but thunar is faster and better.
When nautilus was started it probably killed xfdesktop, also sounds like you then saved your session so nautilus is started when Xfce is. Open a terminal, killall -9 nautilus then hit ALT+F2 and enter xfdesktop. That should cure that, you'll also want to save your Session (Settings> Session and Startup Settings-> tick Prompt on Logout)
For future reference, if you do happen to use nautilus (ick, checkout Thunar!) run it like so; nautilus --no-desktop (maybe it was --nodesktop?)
Sorry for being away for such a long time :-(
But your work-around did it, I'm back in thunar now