Examine source code of World Clock Basic

{
  "manifest_version": 2,
  "name": "World Clock",
  "version": "1.0",
  "description": "World Clock This widget will allow users to view the current time in major cities around the world.",
  "permissions": [],
  "browser_action": {
    "default_popup": "game.html",
    "default_icon": {
      "128": "images/clock-logo.png"
    }
  },
  "icons": {
    "128": "images/clock-logo.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{dc18b172-ad1f-4c25-a32b-a6026f3349ef}"
    }
  }
}