Examine source code of Simple Link Checker

{
  "manifest_version": 2,
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "name": "Link Checker",
  "description": "Redirect Link Checker will check all links on your page to find broken and redirect links",
  "version": "1.1",
  "browser_action": {},
  "icons": {
    "128": "icon.png"
  },
  "applications": {
    "gecko": {
      "id": "@checklinks",
      "strict_min_version": "57.0"
    }
  },
  "permissions": [
    "storage",
    "tabs",
    "activeTab",
    "http://*/*",
    "https://*/*"
  ],
  "web_accessible_resources": [
    "redirectCheck.js"
  ]
}