Examine source code of YouTube Tab Timer

{
  "manifest_version": 2,
  "name": "YouTubeTabTime",
  "version": "7.2",
  "description": "Calculates total watch time of all YouTube tabs",
  "icons": {
    "48": "icons/icon48.png"
  },
  "browser_action": {
    "default_icon": "icons/icon48.png",
    "default_title": "YouTubeTabTime",
    "default_popup": "popup.html"
  },
  "permissions": [
    "tabs",
    "storage",
    "*://*.youtube.com/*"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{9d8d4924-1ae2-4024-a44e-9a71cc1cec01}"
    }
  }
}