Examine source code of Zen Reader

{
  "manifest_version": 3,
  "name": "Zen Reader",
  "version": "0.5.1",
  "description": "Zen Reader declutters pages & reads aloud with highlighting for a calm, distraction-free experience.",
  "browser_specific_settings": {
    "gecko": {
      "id": "zen-reader@francesco.puigdellivol.com",
      "strict_min_version": "109.0"
    }
  },
  "permissions": [
    "activeTab",
    "scripting",
    "storage"
  ],
  "host_permissions": [
    "http://*/*",
    "https://*/*"
  ],
  "action": {
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png"
    },
    "default_title": "Activate Narrative Reader"
  },
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ],
    "type": "module"
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "lib/browser-polyfill.min.js",
        "lib/Readability.js",
        "content.js"
      ],
      "css": [
        "styles.css"
      ],
      "run_at": "document_idle"
    }
  ],
  "web_accessible_resources": [
    {
      "resources": [
        "lib/Readability.js"
      ],
      "matches": [
        "<all_urls>"
      ]
    }
  ],
  "commands": {
    "toggle-reader": {
      "suggested_key": {
        "default": "Ctrl+Shift+R",
        "mac": "Command+Shift+R"
      },
      "description": "Toggle Narrative Reader mode"
    }
  },
  "options_ui": {
    "page": "options.html",
    "open_in_tab": true
  }
}