After I installed XFCE4, the XFCE notifications are being displayed instead of the Unity ones. Even in Unity sessions. How do I set it up so that I get Unity notifications in Unity sessions and XFCE4 notifications in XFCE sessions. If I can't do that, I just want to know how to get the Unity notifications back.
I'm not sure about the first part, but if you don't want to use the Xfce notifications (and thus, use Unity's notifications instead), you can remove the "xfce4-notifyd" package:
Then log out and log back in.