Examine source code of Caffeine - Keep Awake

{
  "manifest_version": 2,
  "version": "0.2.7",
  "name": "Caffeine - Keep Awake",
  "description": "Prevent screen dimming or activating a screen saver by overriding power-saving settings to keep the system or display awake",
  "permissions": [
    "storage",
    "power",
    "idle",
    "contextMenus",
    "alarms",
    "offscreen"
  ],
  "optional_permissions": [
    "downloads"
  ],
  "icons": {
    "16": "/data/icons/16.png",
    "32": "/data/icons/32.png",
    "48": "/data/icons/48.png",
    "64": "/data/icons/64.png",
    "128": "/data/icons/128.png",
    "256": "/data/icons/256.png"
  },
  "background": {
    "scripts": [
      "worker.js"
    ],
    "persistent": false
  },
  "browser_action": {},
  "homepage_url": "https://webextension.org/listing/caffeine.html",
  "commands": {
    "_execute_action": {}
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{4155ed63-3bb7-4939-8d57-574ba4bec1f8}"
    }
  }
}