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