Examine source code of TextToSpeech

{
  "manifest_version": 2,
  "name": "TextToSpeech",
  "version": "1.2.2",
  "description": "Play selected text using TextToSpeech browser API",
  "browser_action": {
    "default_icon": "icons/48.png",
    "default_title": "Text To Speech",
    "default_popup": "popup/index.html"
  },
  "permissions": [
    "activeTab",
    "storage"
  ],
  "icons": {
    "24": "icons/24.png",
    "48": "icons/48.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{3853259c-21a4-4ada-86ef-b8d8dab0b0bb}"
    }
  }
}