Examine source code of Save to Listas

{
  "manifest_version": 2,
  "name": "Save to Listas",
  "version": "0.0.2",
  "description": "The easiest way to add content to Listas",
  "homepage_url": "https://listas.io",
  "icons": {
    "16": "assets/icon16.png",
    "24": "assets/icon24.png",
    "32": "assets/icon32.png",
    "120": "assets/icon120.png",
    "128": "assets/icon128.png"
  },
  "permissions": [
    "tabs",
    "activeTab"
  ],
  "browser_action": {
    "default_title": "Add this page to Listas",
    "default_icon": "assets/icon120.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  }
}