Search for user by attribute no angularfire

I have an application on ionic with angularfire2 in version 5. How do I get the user's UID by email?

Currently, my code looks like this:

const usuariosRef = this.db.list('usuarios/uid', ref => ref.orderByChild('email').equalTo(this.email).limitToFirst(1)).valueChanges();

I save each user by their UID.