Examine source code of Close Tab

{
  "manifest_version": 2,
  "name": "Close Tab Extension",
  "version": "1.0",
  "description": "A simple Firefox extension to close the current tab.",
  "permissions": [
    "tabs"
  ],
  "browser_action": {
    "default_icon": {
      "128": "icon.png"
    },
    "default_title": "Close Current Tab"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "128": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{9d4aeb8f-c58e-43f5-9e3e-1bf89c428a0c}"
    }
  }
}