Examine source code of youtube-speed

{
  "manifest_version": 2,
  "name": "youtube-speed",
  "version": "1.0.0",
  "description": "Extension to modify YouTube playback rate.",
  "permissions": [
    "activeTab"
  ],
  "browser_action": {
    "default_icon": "./assets/icon-48.png",
    "default_title": "Speed",
    "default_popup": "./index.html"
  },
  "icons": {
    "48": "./assets/icon-48.png",
    "96": "./assets/icon-96.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{7bb9fef7-bbb9-435b-971e-0236d868fca5}"
    }
  }
}