Examine source code of YouTube Grid Modifier

{
  "manifest_version": 2,
  "name": "YouTube Grid Modifier",
  "version": "2.0",
  "description": "Forces a specific grid item count on YouTube",
  "permissions": [
    "storage",
    "tabs"
  ],
  "icons": {
    "16": "miasto.png",
    "48": "miasto.png",
    "96": "miasto.png"
  },
  "browser_action": {
    "default_icon": {
      "16": "miasto.png",
      "48": "miasto.png",
      "96": "miasto.png"
    },
    "default_popup": "popup.html",
    "default_title": "Grid Modifier"
  },
  "content_scripts": [
    {
      "matches": [
        "*://www.youtube.com/*"
      ],
      "js": [
        "main.js"
      ],
      "run_at": "document_idle"
    }
  ],
  "applications": {
    "gecko": {
      "id": "youtube-grid@custom.local"
    }
  }
}