Examine source code of Timer Addon

{
  "manifest_version" : 2 ,
  "name" : "Timer Addon",
  "version" : "1.0",
  "description" : "A simple timer addon for Firefox.",
  "icons" : {
    "48" : "icon.png"
  },
  "browser_action" : {
    "default_popup" : "popup.html",
    "default_icon" : "icon.png"
  },
  "background" : {
    "scripts" : [
      "background.js" 
    ],
    "persistent" : true 
  },
  "permissions" : [
    "storage" 
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{8b47a8f7-43a2-4db2-a650-c81b5900f279}"
    }
  }
}