Examine source code of Headers

{
  "manifest_version": 2,
  "name": "Headers",
  "version": "1.1",
  "description": "Fetch and display HTTP response headers for any URL",
  "browser_specific_settings": {
    "gecko": {
      "id": "{fb665f59-7895-414b-bd10-71b74dbefdc3}",
      "strict_min_version": "96.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "icons": {
    "16": "media/n16.png",
    "48": "media/n48.png"
  },
  "browser_action": {
    "default_popup": "display/view.html",
    "default_icon": {
      "16": "media/n16.png",
      "48": "media/n48.png"
    }
  },
  "background": {
    "scripts": [
      "runtime/engine.js"
    ]
  },
  "permissions": [
    "tabs"
  ]
}