Examine source code of 20-20-20 Rule

{
  "name": "20-20-20 Rule",
  "description": "A reminder to look away every 20 minutes at an object that is about 20 feet away for a full 20 seconds.",
  "version": "1.0",
  "manifest_version": 2,
  "icons": {
    "349": "eye.jpg"
  },
  "permissions": [
    "alarms",
    "notifications"
  ],
  "background": {
    "scripts": [
      "main.js"
    ]
  },
  "applications": {
    "gecko": {
      "strict_min_version": "55.0a2"
    }
  }
}