Examine source code of YouTube Items per Row

{
  "manifest_version": 2,
  "name": "YouTube Items Per Row",
  "version": "3.0",
  "description": "Choose how many videos per row on YouTube homepage.",
  "permissions": [
    "storage",
    "https://www.youtube.com/"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://www.youtube.com/*"
      ],
      "js": [
        "content.js"
      ]
    }
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "48": "icon.png"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{73791be5-33b8-41ec-9a20-165724d40bb0}"
    }
  }
}