Examine source code of Frame Timer Extension

{
  "manifest_version": 3,
  "name": "Frame Timer",
  "version": "1.6.3",
  "description": "Calculates the time between 2 frames in a YouTube video",
  "homepage_url": "https://github.com/PottuGD/frame-timer-extension",
  "icons": {
    "48": "icons/logo-48.png",
    "96": "icons/logo-96.png"
  },
  "permissions": [
    "activeTab",
    "storage"
  ],
  "action": {
    "default_icon": "icons/logo-48.png",
    "default_title": "Frame Timer",
    "default_popup": "popup/frame_timer.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "content_script.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "frame-timer@extension"
    }
  }
}