Examine source code of Tab Limiters

{
  "manifest_version": 2,
  "name": "Tab Limiter",
  "version": "1.0",
  "description": "Limit the number of open tabs in Firefox.",
  "permissions": [
    "tabs",
    "storage"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{65179820-8e7c-4cf8-ab97-5706cc8fd135}"
    }
  }
}