Examine source code of Screentime

{
  "manifest_version": 2,
  "name": "Screentime",
  "version": "1.0.1",
  "description": "Definitely one of the tools of all time - this extension tracks time spent on websites.",
  "icons": {
    "48": "iconfolder/iconimage4.png",
    "96": "iconfolder/iconimage4-96.png",
    "128": "iconfolder/iconimage4-128.png"
  },
  "permissions": [
    "tabs",
    "storage"
  ],
  "background": {
    "scripts": [
      "javascriptfiles/screentime.js"
    ],
    "persistent": true
  },
  "browser_action": {
    "default_icon": "iconfolder/iconimage4.png",
    "default_title": "Screentime",
    "default_popup": "htmlfiles/main.html",
    "theme_icons": [
      {
        "light": "iconfolder/iconimage4.png",
        "dark": "iconfolder/iconimage4-light.png",
        "size": 32
      }
    ]
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{9da04cb9-8116-41f5-86eb-e337e20e8416}"
    }
  }
}