Examine source code of H1 Counter

{
  "manifest_version": 3,
  "name": "H1 Counter",
  "version": "1.3.0",
  "description": "Shows the number of <h1> tags on the current page in the toolbar icon. Lists them on click. Displays full <h1> HTML if it contains non-text content.",
  "permissions": [
    "tabs"
  ],
  "host_permissions": [
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "action": {
    "default_title": "H1 Counter",
    "default_popup": "popup.html"
  },
  "icons": {
    "16": "icons/16.png",
    "19": "icons/19.png",
    "32": "icons/32.png",
    "38": "icons/38.png",
    "48": "icons/48.png",
    "64": "icons/64.png",
    "128": "icons/128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "sky_weaver@h1counter",
      "strict_min_version": "109.0"
    }
  }
}