Examine source code of Quick Tab Closer

{
  "manifest_version": 2,
  "name": "Quick Tab Closer",
  "version": "1.0",
  "description": "Close the current tab instantly with a single click.",
  "permissions": [
    "tabs"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_title": "Close Tab"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{527a55df-47a2-4412-9962-e4ef433b6052}"
    }
  }
}