Examine source code of Sleep Timer Fixxi

{
  "manifest_version": 2,
  "name": "Sleep Timer Fix",
  "version": "1.0.3",
  "description": "Put any tab on a sleep timer to close or mute the tab when the timer expires.",
  "permissions": [
    "tabs",
    "alarms"
  ],
  "background": {
    "scripts": [
      "./background.js"
    ]
  },
  "icons": {
    "16": "icons/icon-16.png",
    "32": "icons/icon-32.png",
    "48": "icons/icon-48.png",
    "64": "icons/icon-64.png",
    "96": "icons/icon-96.png",
    "128": "icons/icon-128.png",
    "256": "icons/icon-256.png"
  },
  "browser_action": {
    "default_icon": {
      "16": "icons/icon-16.png",
      "32": "icons/icon-32.png",
      "48": "icons/icon-48.png",
      "64": "icons/icon-64.png",
      "96": "icons/icon-96.png",
      "128": "icons/icon-128.png",
      "256": "icons/icon-256.png"
    },
    "default_popup": "popup/popup.html",
    "default_title": "Sleep Timer"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{20c4423f-4a6b-4598-bf1b-38fabf5bb435}"
    }
  }
}