> I love Firebase Authentication, it's such an easy way to add auth to side projects.

It's easy to use but it adds 55kB gzip to your project.

https://bundlephobia.com/result?p=@firebase/auth@0.16.4

A couple of comments on the Svelte code.

1) It doesn't makes much sense to use onMount() with listenForAuthChanges(). Just modify the currentUser writable whenever onAuthStateChanged() has an update. Now simply import and use $currentUser in your components.

2) You don't need to use currentUser.subscribe() from your .svelte files as you can use the reactive $: notation for this. You can, if it makes more sense to you, but I wouldn't say it's idiomatic.