Firefox icon does not stick in launcher!

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http://askubuntu.com – Intentionally or accidentally I have removed Firefox from Unity launcher. When I opened Firefox to get the icon on launcher so that I can right-click it and choose "Keep on launcher" When I did so, the icon stays for the session, but when I logged out and return again, I don't see the icon on launcher. How can I keep Firefox icon on launcher?! (HowTos)