Examine source code of Sun, clouds, rain

{
  "manifest_version": 2,
  "name": "Weather forecast icon",
  "version": "1.0",
  "description": "The weather forecast icon predicts light showers with sunshine, or a day with mixed rain and sunshine. The cloud expression adds to the emotional tone – perhaps a mix of sadness and hope.",
  "icons": {
    "48": "icon.png"
  },
  "browser_action": {
    "default_icon": "icon.png",
    "default_popup": "popup.html",
    "default_title": "Click me!"
  },
  "permissions": [
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{a3960739-19dd-4c20-8399-c6c475ab5a9c}"
    }
  }
}