Examine source code of TrackPageTime

{
  "manifest_version": 2,
  "name": "TrackPageTime",
  "description": "Displays a sidebar with a stop-watch for how long you've been in a website and the specific url. All time tracking is local to the web browser and your information is private!",
  "version": "2.4",
  "browser_action": {
    "default_icon": "icons/hourglass-lite2.png",
    "theme_icons": [
      {
        "light": "icons/hourglass-lite2.png",
        "dark": "icons/hourglass-lite2.png",
        "size": 38
      }
    ],
    "default_title": "TimeTracker",
    "default_popup": "sidebar/panel.html"
  },
  "background": {
    "scripts": [
      "sidebar/background.js"
    ],
    "persistent": true
  },
  "permissions": [
    "storage",
    "tabs",
    "scripting",
    "idle",
    "activeTab"
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{75fce223-b5bd-49dd-ada7-12cf69b78a70}"
    }
  }
}