Examine source code of Text to Speech

{
  "sidebar_action": {
    "default_icon": "icons/icon128.png",
    "default_title": "Text to Speech",
    "default_panel": "data/index.html"
  },
  "applications": {
    "gecko": {
      "id": "jid1-BpiWzS8B6zZrzg@jetpack",
      "strict_min_version": "57.0"
    }
  },
  "content_security_policy": "script-src 'self'; object-src 'self'",
  "description": "Selected text and click in context menu 'Selected text to Speech' to listen",
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "manifest_version": 2,
  "name": "Text to Speech",
  "web_accessible_resources": [
    "data/*"
  ],
  "permissions": [
    "contextMenus",
    "storage"
  ],
  "version": "1.5.2"
}