Examine source code of Highlight Text to speech

{
  "manifest_version": 2,
  "name": "Text-to-Speech Extension",
  "version": "1.0.1",
  "description": "Read text aloud on any webpage by highlighting it.",
  "icons": {
    "48": "icon.png"
  },
  "permissions": [
    "activeTab",
    "storage",
    "tabs"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icon.png"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{a8a71501-51b1-4d2c-aa81-7a1a94e214cf}"
    }
  }
}