Examine source code of Print Image Pro

{
  "manifest_version": 2,
  "name": "Print Image Pro",
  "version": "2.2",
  "description": "This extension allows you to scale an image to fit the page before printing it.",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "contextMenus"
  ],
  "icons": {
    "16": "icon.png",
    "128": "icon-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{53e47258-7e5d-4a3e-afe8-b3b3f20434f7}"
    }
  }
}