Examine source code of Tab Counter Plus

{
  "name": "Tab Counter Plus",
  "short_name": "Tab Counter",
  "author": "Oriol Brufau",
  "homepage_url": "https://github.com/Loirooriol/tab-counter-plus",
  "version": "3.4",
  "description": "Shows the number of tabs in each window. Efficient and customizable.",
  "manifest_version": 2,
  "applications": {
    "gecko": {
      "id": "tab-counter-plus@Loirooriol",
      "strict_min_version": "63.0"
    }
  },
  "icons": {
    "16": "icon16.gif",
    "64": "icon.svg"
  },
  "permissions": [
    "storage"
  ],
  "browser_action": {
    "default_icon": {
      "16": "icon16.gif",
      "64": "icon.svg"
    },
    "default_popup": "popup.html"
  },
  "options_ui": {
    "page": "options.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  }
}