您无法删除验证码验证默认身份验证。

使用匿名身份验证，以避免出现 captcha 字母。另外匿名身份验证比 Firebase身份验证默认身份验证。

Use anonymous authentication to avoid captcha letters to appear. Also anonymous authentication is more simpler than Firebase Authentication default authentication.

用法：

firebase.auth().signInAnonymously().catch(function(error) {
  // Handle Errors here.
  var errorCode = error.code;
  var errorMessage = error.message;
  // ...
});

详情请参阅此官方文档： https://firebase.google.com/docs/auth/web/anonymous-auth

For details please follow this official documentation : https://firebase.google.com/docs/auth/web/anonymous-auth