Examine source code of Simple Reader Mode

{
  "manifest_version": 2,
  "name": "Simple Reader Mode",
  "version": "1.0",
  "description": "Switch the current page to reader mode if supported.",
  "permissions": [
    "activeTab",
    "notifications"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{cd6ba91e-6349-4a98-b577-31d477d4ac03}"
    }
  }
}