Examine source code of Save for later

{
  "manifest_version": 2,
  "name": "Save for later",
  "version": "1.2.1",
  "description": "Save tabs in window to be used later",
  "icons": {
    "36": "icons/main-36.png",
    "48": "icons/main-48.png",
    "64": "icons/main-64.png",
    "96": "icons/main-96.png",
    "128": "icons/main-128.png"
  },
  "permissions": [
    "tabs",
    "storage"
  ],
  "background": {
    "scripts": [
      "node_modules/webextension-polyfill/dist/browser-polyfill.min.js",
      "background-script.js"
    ]
  },
  "browser_action": {
    "default_icon": "icons/main-64.png",
    "default_title": "Save for later",
    "default_popup": "popup/main.html",
    "browser_style": true
  },
  "offline_enabled": true,
  "browser_specific_settings": {
    "gecko": {
      "id": "{6a60f9d9-12c8-40bb-93a8-5ccd950de746}"
    }
  }
}