Examine source code of TubeLink

{
  "manifest_version": 2,
  "name": "TubeLink",
  "version": "1.1resigned1",
  "description": "Download YouTube videos quickly and easily! Supports all available YouTube formats (MP4, FLV, WebM, 3GP) for any video quality (from 144p up to 3072p). How it works - It simply adds a 'Download' button which populates a list with all the available videos to download. To download a YouTube video - whenever you're on a video page in YouTube, you'll see the 'Download' button with a round red icon in it, click that button to populate the list of all available formats to download, click the desired format, save to your hard drive and that's it! This is an easy YouTube Video Downloader - If all you need is a simple, intuitive, and non-intrusive Add-On to download YouTube videos, this is the Add-On for you. 1-Click YouTube Video Downloader is a great Download Helper Tool and is a great combination with Video DownloadHelper , DownThemAll and FlashGot. Soon you could Download YouTube videos directly from the search results of Google, Yahoo and Bing.",
  "homepage_url": "https://webrikk.com",
  "icons": {
    "16": "icons/icon16.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "tubelink.js"
      ]
    }
  ],
  "permissions": [
    "tabs"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{08bb274f-71f0-4492-9d1e-65874d16cced}"
    }
  }
}