Examine source code of Background Image Explorer

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "manifest_version": 2,
  "name": "Background Image Explorer",
  "version": "1.0.3",
  "description": "This add-on extends the functionality of the Firefox browser by adding a menu item that allows you to open a background image in a new tab. When you right-click a location on a web page, the extension identifies the closest element that contains a background image and provides the option to open that image in a new tab, making it easy to access and view. background image of the website conveniently.",
  "permissions": [
    "contextMenus",
    "<all_urls>"
  ],
  "background": {
    "persistent": false,
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "js": [
        "content.js"
      ],
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_start"
    }
  ],
  "icons": {
    "16": "icons/16.png",
    "48": "icons/48.png",
    "128": "icons/128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{b0cd7ea6-987c-4bda-aa5f-cd1005d7ab11}"
    }
  }
}