Examine source code of Reading Mode

{
  "manifest_version": 2,
  "name": "Reading Mode",
  "description": "Improve readability on any website. Larger fonts, better spacing, warm backgrounds, distraction-free layout. Free.",
  "version": "1.0.0",
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "permissions": [
    "activeTab",
    "storage",
    "scripting",
    "tabs",
    "<all_urls>"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_title": "Transformer",
    "default_popup": "popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "run_at": "document_start",
      "js": [
        "content-scripts/content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "reading-mode@saasinsiders.com",
      "data_collection_permissions": {
        "required": [
          "personallyIdentifyingInfo"
        ],
        "optional": [
          "technicalAndInteraction"
        ]
      }
    }
  }
}