Examine source code of Tab Close Confirmation

{
  "manifest_version": 2,
  "name": "Tab Close Confirmation",
  "version": "1.0",
  "description": "Asks for confirmation before closing a tab.",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "permissions": [
    "tabs"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{361326f9-840d-4d98-8d14-1abeac511352}"
    }
  }
}