Examine source code of Weather Widget yours

{
  "manifest_version": 2,
  "name": "Weather Widget",
  "version": "1.0",
  "description": "Simple weather information widget",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Weather Widget"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{8999fd03-d257-4631-90e4-5f15094eaf32}"
    }
  }
}