How do I remove a hosted site from firebase

It can be deleted.

1. Run firebase hosting:disable through the firebase-tools CLI first.
2. Go to Firebase Console and select Hosting from the menu of the left.
3. You will see the deployed project with a list of your historical actions like Deployed, disabled, etc.
4. Only after you have disabled the site, the "three vertical dots" menu will be available for you to choose the action to delete the deployment.

You don't need to upload empty directory.

Just open your project's root directory and enter the following command

$ firebase hosting:disable
? Are you sure you want to disable Firebase Hosting for the site xyz
This will immediately make your site inaccessible! Yes
✔  Hosting has been disabled for xyz. Deploy a new version 
to re-enable.

This will instantly disable running website also adds a Disabled status in release history. Tested on firebase CLI version 9.20.0

If you have multiple site hosted in same project, then use -s flag to specify the site you want to disable.

firebase hosting:disable -s yoursitename

It's a bit hidden, but here are the steps:

1. Go to the Firebase Hosting console for your project, you will see your domain.
2. Hover over your domain. There's an overflow menu (⋮ three vertical dots) on the right.
3. From the overflow menu select Delete Domain