Examine source code of mainpage

{
  "manifest_version": 2,
  "name": "mainpage",
  "version": "1.0",
  "description": "Changes the URL of a tab to the main page of the website.",
  "homepage_url": "https://github.com/simonthor/mainpage",
  "permissions": [
    "activeTab"
  ],
  "icons": {
    "48": "icons/icon.svg",
    "96": "icons/icon.svg"
  },
  "background": {
    "scripts": [
      "mainpage.js"
    ]
  },
  "browser_action": {
    "default_icon": "icons/icon.svg"
  }
}