Examine source code of Back To Close

{
  "manifest_version": 3,
  "name": "Back To Close",
  "description": "Browser extension that closes the active tab when navigating back on the first history entry",
  "version": "1.0.0",
  "icons": {
    "16": "icon/16.png",
    "32": "icon/32.png",
    "48": "icon/48.png",
    "64": "icon/64.png",
    "128": "icon/128.png",
    "256": "icon/256.png"
  },
  "permissions": [
    "storage",
    "tabs",
    "scripting"
  ],
  "action": {
    "default_icon": {
      "128": "icon/128.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "back-to-close@lth"
    }
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [],
  "host_permissions": [
    "<all_urls>"
  ]
}