Examine source code of Advanced Site Checker

{
  "name": "Advanced Site Checker",
  "applications": {
    "gecko": {
      "id": "admin@advanced-site-checker.com",
      "strict_min_version": "48.0"
    }
  },
  "version": "0.8.2",
  "description": "Ultimate tool to improve your site.",
  "manifest_version": 2,
  "permissions": [
    "tabs"
  ],
  "browser_action": {
    "default_icon": "favicon.png",
    "default_title": "Check page",
    "browser_style": true
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "icons": {
    "48": "favicon.png",
    "96": "favicon-96.png",
    "128": "favicon-128.png"
  }
}