Examine source code of Board Centralizer

{
  "manifest_version": 2,
  "name": "Board Centralizer",
  "version": "2.0",
  "description": "Centralize every chessboard on all chess.com webpages.",
  "icons": {
    "128": "/icons/9055285_bxs_chess_icon128px.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.chess.com/puzzles*",
        "*://*.chess.com/play*",
        "*://*.chess.com/game*"
      ],
      "js": [
        "app.js"
      ]
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{2cece0d4-2840-4da3-865e-e862ac849bf6}"
    }
  }
}