Examine source code of Snek 2 - A Snake Game

{
  "manifest_version": 2,
  "name": "Snek 2 - A snake game",
  "version": "2.7.2",
  "description": "A simple Snake game as a Firefox extension",
  "icons": {
    "48": "icon.png"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "browser_action": {
    "default_icon": {
      "48": "icon.png"
    },
    "default_title": "Play Snek 2"
  },
  "options_ui": {
    "page": "index.html",
    "open_in_tab": true,
    "browser_style": false
  },
  "permissions": [
    "storage"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{dea03ec1-b728-4824-a049-bdf7c1700619}",
      "strict_min_version": "140.0",
      "data_collection_permissions": {
        "required": [
          "none"
        ]
      }
    },
    "gecko_android": {
      "strict_min_version": "142.0"
    }
  }
}