Examine source code of Wallpaper Snapper

{
  "manifest_version": 2,
  "name": "Wallpaper Snapper",
  "version": "1.0",
  "description": "Save the current image instantly as your desktop wallpaper.",
  "permissions": [
    "downloads",
    "activeTab",
    "<all_urls>"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{5da78299-02b6-4cbc-8c7f-66e70f377b4c}"
    }
  }
}