No indication from Load From Pontoon button if user is not signed in

[functionzz]

Steps to reproduce

1. Reinstall Pontoon Add-on from addons.mozilla.org. Do not sign in.
2. From the Introduction Tour, click Addon Settings.
3. Observe that when the Load From Pontoon button is clicked, it does nothing.

Expected Behaviour

There should be a way to acknowledge that the user is not logged in before accessing the Load From Pontoon button, or lock the settings page behind a login page. That is because the Load From Pontoon button gets the user's homepage locale preference on Pontoon which does not exist if the user is not logged in.