Firebase namespace not found in Unity

When I'm trying to build my unity project for WebGL, I'm getting the below error. I don't get this error when I'm trying to build for Android. The type or namespace name 'Firebase' could not be found (are you missing a using directive or an assembly reference?) The type or namespace name 'FirebaseAuth' could not be found (are you missing a using directive or an assembly reference?) I"m using Unity 2018.4.10f1 Appreciate any help to resolve this.