Examine source code of Element Outliner

{
  "manifest_version": 2,
  "name": "Element Outliner",
  "version": "1.0.0",
  "description": "Highlight elements on hover and show info on click.",
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "128": "icons/icon-128.png"
  },
  "permissions": [
    "tabs",
    "storage",
    "activeTab"
  ],
  "browser_action": {
    "default_title": "Element Outliner",
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon-16.png",
      "32": "icons/icon-32.png",
      "48": "icons/icon-48.png",
      "128": "icons/icon-128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "strict_min_version": "109.0",
      "id": "{a2fcd155-3af9-4aca-b82e-b15c18d90146}"
    }
  }
}