Examine source code of Weather Lookup

{
  "manifest_version": 2,
  "name": "Weather Lookup",
  "version": "1.0",
  "description": "Get the current weather for your city.",
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon.png"
    }
  },
  "permissions": [
    "activeTab",
    "https://api.openweathermap.org/"
  ],
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{4a58bc87-bf72-4f73-af33-e266879da133}"
    }
  }
}