Examine source code of ESPN Custom Logos

{
  "manifest_version": 3,
  "name": "ESPN Custom Logos",
  "version": "1.0.0",
  "description": "Upload custom images for your fantasy team logos",
  "permissions": [
    "cookies"
  ],
  "host_permissions": [
    "*://fantasy.espn.com/*",
    "*://*.fantasy.espn.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "*://fantasy.espn.com/*",
        "*://*.fantasy.espn.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "@espn-custom-logos.darkonda"
    }
  }
}