Examine source code of YouTubeTooltip

{
  "manifest_version": 2,
  "name": "YouTubeTooltip",
  "version": "1.1.0",
  "icons": {
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "description": "Adds a tooltip to YouTube links containing the title, duration, and viewcount of the video",
  "permissions": [
    "<all_urls>"
  ],
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "youtubetooltip.js"
      ]
    }
  ]
}