Examine source code of Video Timer

{
  "name": "Video Timer",
  "version": "1.1.1",
  "manifest_version": 3,
  "description": "Timing Youtube and Twich videos",
  "permissions": [
    "storage",
    "tabs",
    "activeTab",
    "scripting"
  ],
  "host_permissions": [
    "*://www.youtube.com/watch*",
    "*://www.twitch.tv/videos/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "action": {
    "default_icon": {
      "48": "round_av_timer_black_48dp.png"
    },
    "default_title": "Click to activate timer window"
  },
  "icons": {
    "48": "round_av_timer_black_48dp.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "video-timer@noahkra"
    }
  }
}