Fire.app can't be opened because it is from an unindentified developer on Mac OSX 10.8

If you encounter Fire.app can't be opened because it is from an unidentified developer on Mac OSX 10.8, please refer to following instructions.

This is due to settings from "Security and privacy". Please open "System Preferences", then click on "Security & Privacy":

To edit the security settings, you must first click the padlock icon in the bottom left of the window, then change "Allow applications downloaded from" to "Anywhere":

That's it! You may now start Fire.app!