Examine source code of YouTube Observer

{
  "name": "YouTube Observer",
  "description": "Hide progress bar / duration when watching YouTube videos",
  "version": "0.3",
  "manifest_version": 2,
  "content_scripts": [
    {
      "matches": [
        "https://*.youtube.com/*"
      ],
      "run_at": "document_start",
      "js": [
        "contentScript.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "serviceWorker.js"
    ]
  },
  "permissions": [
    "storage"
  ],
  "browser_action": {
    "default_icon": "images/icon.png",
    "default_popup": "popup.html"
  }
}