Examine source code of Site Metrics

{
  "manifest_version": 2,
  "name": "Site Metrics",
  "version": "1.2.2",
  "description": "Instant statistics: words, links, images and load time",
  "browser_specific_settings": {
    "gecko": {
      "id": "{25ecf9f6-4048-407b-acf1-faa702b109a5}",
      "strict_min_version": "96.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  },
  "icons": {
    "16": "media/n16.png",
    "32": "media/n32.png",
    "48": "media/n48.png",
    "96": "media/n96.png",
    "128": "media/n128.png"
  },
  "browser_action": {
    "default_popup": "display/view.html",
    "default_icon": {
      "16": "media/n16.png",
      "32": "media/n32.png",
      "48": "media/n48.png",
      "96": "media/n96.png",
      "128": "media/n128.png"
    }
  },
  "background": {
    "scripts": [
      "runtime/engine.js"
    ]
  },
  "permissions": [
    "tabs",
    "activeTab"
  ]
}