Examine source code of YouTube SmartPlay

{
  "manifest_version": 2,
  "name": "YouTube SmartPlay",
  "version": "1.2.4resigned1",
  "description": "Synchronizes playback between multiple YouTube and Vimeo tabs: video is paused when switched to another tab that also plays.",
  "author": "Mutum Malemnganba",
  "permissions": [
    "tabs",
    "webNavigation"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://*.youtube.com/watch?v=*",
        "https://*.youtube.com/channel/*",
        "https://*.youtube.com/user/*",
        "https://*.youtube.com/",
        "https://*.youtube.com/results?*",
        "https://vimeo.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": "images/icon-48.png",
    "default_popup": "popup.html",
    "default_title": "YouTube SmartPlay"
  },
  "icons": {
    "16": "images/icon-16.png",
    "48": "images/icon-48.png",
    "128": "images/icon-128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{8be37b57-a577-446b-b02e-ab7e0b74ae16}"
    }
  }
}