CentOS DesktopEntry

 IBM Developer  :  https://www.ibm.com/developerworks/cn/linux/l-cn-dtef/index.html

[Desktop Entry]
Name=firefox
Comment=firefox
Exec=/usr/local/firefox/firefox
Icon=/usr/local/firefox/browser/chrome/icons/default/default128.png
Type=Application
StartupNotify=true
Categories=Network  #category on menu

about Categoruies: 

cat /etc/xdg/menus/application.menu

cd /usr/share/desktop-directories

http://www.jb51.net/os/RedHat/523235.html