Examine source code of Heartify

{
  "manifest_version": 3,
  "name": "Heartify",
  "version": "1.0.13",
  "description": "Returns hearts back to Spotify!",
  "icons": {
    "16": "/icons/icon16.png",
    "32": "/icons/icon32.png",
    "48": "/icons/icon48.png",
    "128": "/icons/icon128.png"
  },
  "permissions": [
    "webRequest",
    "storage"
  ],
  "host_permissions": [
    "https://open.spotify.com/*",
    "https://api-partner.spotify.com/*",
    "https://spclient.wg.spotify.com/*"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "https://open.spotify.com/*"
      ],
      "js": [
        "content.js"
      ],
      "run_at": "document_start"
    },
    {
      "matches": [
        "https://open.spotify.com/*"
      ],
      "js": [
        "inject.js"
      ],
      "world": "MAIN",
      "run_at": "document_start"
    }
  ],
  "web_accessible_resources": [
    {
      "resources": [
        "/assets/heart_unfilled.svg",
        "/assets/heart_filled.svg"
      ],
      "matches": [
        "https://open.spotify.com/*"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "heartify@moma.rs",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    }
  }
}