Examine source code of Strava Custom Maps

{
  "manifest_version": 3,
  "name": "Strava Custom Maps",
  "version": "1.1",
  "description": "Unlocks Custom Maps (Mapy.cz, etc.) for Strava.",
  "browser_specific_settings": {
    "gecko": {
      "id": "strava-custom-maps@just4d3v.com",
      "strict_min_version": "142.0"
    }
  },
  "permissions": [
    "declarativeNetRequest",
    "scripting"
  ],
  "host_permissions": [
    "*://*.strava.com/*",
    "*://*.mapy.cz/*",
    "*://*.geoportail.gouv.fr/*"
  ],
  "declarative_net_request": {
    "rule_resources": [
      {
        "id": "rules_mapy",
        "enabled": true,
        "path": "rules.json"
      }
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.strava.com/*"
      ],
      "js": [
        "content.js"
      ],
      "css": [
        "styles.css"
      ],
      "run_at": "document_start"
    }
  ],
  "web_accessible_resources": [
    {
      "resources": [
        "injected_unlock.js",
        "layers_config.js",
        "injected_maps_builder.js",
        "injected_maps_activity.js",
        "leaflet.js",
        "leaflet.css"
      ],
      "matches": [
        "*://www.strava.com/*"
      ]
    }
  ]
}