Examine source code of Tab Restrictor

{
  "manifest_version": 2,
  "name": "Tab Limit",
  "version": "1.0",
  "description": "Limit the number of tabs",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{c910d00f-1e60-42ec-8de7-a6b0b1019149}"
    }
  }
}