In which folder should I place a desktop file that I want to be showed...on the desktop of every user

Hello.

I'm trying to understand where should I place a desktop file like the one below (its the desktop file that when clicked will run Firefox) because I want that it is placed on the desktop of every user created by who will use my customized distro (with cubic) when it will be ready. So,for example,if he will create the user john,I would like that it will be placed on the folder /home/john/Desktop such as in /root/Desktop and even on the Desktop folder of the live user. I've placed it on /etc/skel such as on /etc/skel/.config or /etc/xdg and on /etc/xdg/.config during the customization of xubuntu with cubic,but I didn't see it on the desktop folder of the live user. So these aren't the right place where to save it.

[Desktop Entry]
Version=1.0
Name=Firefox Web Browser
Exec=firefox %u
Terminal=false
X-MultipleArgs=false
Type=Application
Icon=firefox
Categories=GNOME;GTK;Network;WebBrowser;
MimeType=text/html;text/xml;application/xhtml+xml;application/xml;application/rss+xml;application/rdf+xml;image/gif;image/jpeg;image/png;x-scheme-handler/http;x-scheme-handler/https;x-scheme-handler/ftp;x-scheme-handler/chrome;video/webm;application/x-xpinstall;
StartupNotify=true
Actions=new-window;new-private-window;

[Desktop Action new-window]
Name=Open a New Window
Exec=firefox -new-window

[Desktop Action new-private-window]
Name=Open a New Private Window
Exec=firefox -private-window