Examine source code of ResumeTube (YouTube)

{
  "manifest_version": 2,
  "name": "ResumeTube",
  "version": "1.1",
  "description": "Save a video's current playback time and resume later.",
  "permissions": [
    "storage",
    "tabs",
    "activeTab"
  ],
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "16": "icons/icon16.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*",
        "*://youtu.be/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "resumetube@taskturtles"
    }
  }
}