Examine source code of Tab Limit

{
  "manifest_version": 2,
  "name": "Tab Limit",
  "version": "0.3.1",
  "description": "Limit the number of open tabs – in total and per window",
  "author": "Matthias Vogt, Armand Grillet",
  "homepage_url": "https://github.com/armandgrillet/tab-limit",
  "icons": {
    "48": "icons/48.png",
    "128": "icons/128.png"
  },
  "browser_action": {
    "default_icon": {
      "48": "icons/48.png",
      "128": "icons/128.png"
    },
    "default_title": "Tab Limit",
    "default_popup": "options.html",
    "theme_icons": [
      {
        "light": "icons/48.png",
        "dark": "icons/48-dark.png",
        "size": 48
      },
      {
        "light": "icons/128.png",
        "dark": "icons/128-dark.png",
        "size": 128
      }
    ]
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": false
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "tablimit@tablimiter"
    }
  }
}