Examine source code of Web Feed Subscription Button

{
  "name": "Web Feed Subscription Button",
  "description": "Show a button if the page you are viewing has a feed to which you can subscribe.",
  "version": "1.0.0",
  "manifest_version": 3,
  "action": {
    "default_icon": "/assets/rss.png",
    "default_title": "Subscribe to this website"
  },
  "page_action": {
    "default_icon": "/assets/rss.png",
    "default_title": "Subscribe to this website"
  },
  "permissions": [
    "tabs",
    "activeTab",
    "storage"
  ],
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  },
  "background": {
    "service_worker": "background.js",
    "scripts": [
      "background.js"
    ],
    "type": "module"
  },
  "host_permissions": [
    "<all_urls>"
  ],
  "options_page": "options.html",
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "app.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "web-feed-subscriber@capjamesg"
    }
  }
}