~/.config/xfce4/xinitrc
User configuration file
Initialize an xfce session
startxfce4
startxfce4 is a script responsible for starting an Xfce session. It runs xinit passing the file specified in the FILES subsection as an argument.
You may want to modify the default xinitrc file. In order to do that, copy /etc/xdg/xfce4/xinitrc to ~/.config/xfce4/xinitrc and modify that file.
~/.config/xfce4/xinitrc
User configuration file
/etc/xdg/xfce4/xinitrc
System wide configuration file