I am using Webpack with firebase and firebase-admin.
To install firebase I ran
npm install --save firebase
I am importing firebase
I didn't need to delete my node_modules folder. Just confirm if you've both '@firebase' and 'firebase' subfolders inside node_mudules. If you do, change the path to 'firebase' on your require statement to './node_modules/firebase'
and make the next line; require('./node_modules/firebase/firebase-auth');