Examine source code of Too Many Tabs

{
  "browser_specific_settings": {
    "gecko": {
      "id": "to-many-tabs@fabianmoronzirfas.me",
      "strict_min_version": "79.0"
    }
  },
  "manifest_version": 2,
  "name": "Too Many Tabs",
  "short_name": "2ManyTabs",
  "description": "This extension will notify you when you have more then n tabs open",
  "version": "1.0.4",
  "author": "Fabian Morón Zirfas",
  "icons": {
    "16": "icon16.png",
    "48": "icon48.png",
    "128": "icon128.png"
  },
  "browser_action": {
    "default_icon": {
      "19": "icon19.png",
      "38": "icon38.png"
    },
    "default_popup": "popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": false
  },
  "options_ui": {
    "page": "options.html",
    "browser_style": true
  },
  "permissions": [
    "activeTab",
    "tabs",
    "storage",
    "notifications"
  ]
}