Examine source code of Text to Speech

{
  "manifest_version": 2,
  "version": "0.1.2",
  "name": "Text to Speech",
  "description": "Read any selected text in the browser with human-quality text-to-speech (TTS) engines",
  "permissions": [
    "storage",
    "activeTab",
    "notifications"
  ],
  "background": {
    "persistent": false,
    "scripts": [
      "background.js"
    ]
  },
  "homepage_url": "https://add0n.com/text-to-speech.html",
  "icons": {
    "16": "data/icons/16.png",
    "19": "data/icons/19.png",
    "32": "data/icons/32.png",
    "38": "data/icons/38.png",
    "48": "data/icons/48.png",
    "64": "data/icons/64.png",
    "128": "data/icons/128.png",
    "256": "data/icons/256.png"
  },
  "browser_action": {
    "default_icon": {
      "16": "data/icons/16.png",
      "19": "data/icons/19.png",
      "32": "data/icons/32.png",
      "38": "data/icons/38.png",
      "48": "data/icons/48.png",
      "64": "data/icons/64.png"
    },
    "default_title": "Select some text and press the icon to display the TTS popup. Click once more to hide the popup"
  }
}