Examine source code of BlockMailAdv

{
  "browser_specific_settings": {
    "gecko": {
      "id": "neowit@pochta.com",
      "strict_min_version": "42.0"
    }
  },
  "manifest_version": 3,
  "name": "BlockMailAdv",
  "version": "0.1",
  "permissions": [
    "scripting",
    "activeTab"
  ],
  "host_permissions": [
    "http://www.blogger.com/*",
    "http://*.google.com/*"
  ],
  "content_scripts": [
    {
      "matches": [
        "https://*.mail.ru/*"
      ],
      "js": [
        "script.js"
      ],
      "css": [
        "style.css"
      ]
    }
  ]
}