Examine source code of Reader Mode Enhancer

{
  "manifest_version": 2,
  "name": "Reader Mode Enhancer",
  "version": "1.0",
  "description": "Enhances Firefox's built-in Reader Mode with custom styles.",
  "permissions": [
    "activeTab",
    "tabs",
    "storage"
  ],
  "browser_action": {
    "default_icon": "icons/icon-48.png",
    "default_title": "Enhance Reader Mode",
    "default_popup": "popup/popup.html"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "48": "icons/icon-48.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{b208c71a-4875-4823-b6ca-66ef0c5fb246}"
    }
  }
}