Examine source code of Pomofocus Launcher

{
  "manifest_version": 2,
  "name": "Pomofocus Launcher",
  "version": "1.0",
  "description": "Embed Pomofocus.io as a toolbar app.",
  "browser_action": {
    "default_popup": "popup.html",
    "default_icon": {
      "48": "icons/pomodoro.png"
    }
  },
  "permissions": [],
  "icons": {
    "48": "icons/pomodoro.png"
  },
  "applications": {
    "gecko": {
      "id": "pomofocus-launcher@example.com",
      "strict_min_version": "68.0"
    }
  }
}