Examine source code of Quick 2048

{
  "name": "Quick 2048",
  "description": "Play 2048 from firefox",
  "homepage_url": "https://rejahrehim.com/quick-2048",
  "developer": {
    "name": "Rejah Rehim",
    "url": "https://rejahrehim.com"
  },
  "manifest_version": 2,
  "icons": {
    "16": "quick-2048-16.png",
    "32": "quick-2048-32.png",
    "64": "quick-2048-64.png",
    "128": "quick-2048-128.png"
  },
  "browser_action": {
    "browser_style": true,
    "default_title": "Quick 2048",
    "default_icon": {
      "16": "quick-2048-16.png",
      "32": "quick-2048-32.png",
      "64": "quick-2048-64.png",
      "128": "quick-2048-128.png"
    },
    "default_popup": "popup/app.html"
  },
  "version": "2.1resigned1",
  "applications": {
    "gecko": {
      "strict_min_version": "57.0a1",
      "id": "@quick-2048"
    }
  }
}