Examine source code of Download Imagei

{
  "name": "Download Imagei",
  "description": "Displays all webpage images and allows user to download",
  "version": "1.8",
  "manifest_version": 2,
  "page_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "/images/download_image16.png",
      "32": "/images/download_image32.png",
      "48": "/images/download_image48.png",
      "128": "/images/download_image128.png"
    }
  },
  "icons": {
    "16": "/images/download_image16.png",
    "32": "/images/download_image32.png",
    "48": "/images/download_image48.png",
    "128": "/images/download_image128.png"
  },
  "permissions": [
    "downloads",
    "storage",
    "activeTab",
    "declarativeContent"
  ],
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "options_page": "options.html",
  "browser_specific_settings": {
    "gecko": {
      "id": "{dbd99fa2-be42-4767-b7d1-79af8b1e5269}"
    }
  }
}