Examine source code of Undo Closed Tabs Button

{
  "manifest_version": 2,
  "name": "Undo Closed Tabs Button",
  "version": "1.0",
  "description": "Quickly restore recently closed tabs.",
  "permissions": [
    "tabs",
    "sessions",
    "storage",
    "<all_urls>",
    "declarativeNetRequestWithHostAccess"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icon.png"
    }
  },
  "icons": {
    "16": "icon.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "persistent": true
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content_script.js"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{522502e2-c13b-47bb-9703-b9a063633bfb}"
    }
  }
}