Examine source code of firelocks

{
  "name": "firelocks",
  "description": "firelocks is swaylock inspired extension that allows you to hide your password length in form",
  "version": "0.1",
  "manifest_version": 2,
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "main.js"
      ],
      "css": [
        "main.css"
      ],
      "run_at": "document_end"
    }
  ],
  "browser_specific_settings": {
    "gecko": {
      "id": "{518cd226-32cb-4585-9f84-4310823700bd}"
    }
  }
}