Examine source code of CSS and XPath checker

{
  "manifest_version": 3,
  "name": "CSS and XPath checker",
  "description": "A helper tool for to confirm CSS and XPath selector.",
  "version": "0.25.1",
  "icons": {
    "16": "icon/16.png",
    "48": "icon/48.png",
    "128": "icon/128.png"
  },
  "permissions": [
    "tabs"
  ],
  "host_permissions": [
    "http://*/*",
    "https://*/*"
  ],
  "action": {
    "default_title": "CSS and XPath Checker",
    "default_popup": "popup.html"
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "takaki-cxchecker@example.com"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "http://*/*",
        "https://*/*"
      ],
      "js": [
        "content-scripts/content.js"
      ]
    }
  ]
}