First boot: accessing FreedomBox on a VM from browser

A twitter user has tested FreedomBox by installing it on a VM. He initially had some trouble accessing plinth and rightly observed that our documentation regarding VM's needs some work.

He eventually discovered that the issue was with Firefox.

The problem: FreedomBox could be accessed at https://freedombox/plinth using Chrome browser but NOT firefox.

Here are the details I've gathered:

1. User was running FreedomBox on a VM on his machine
2. User tried to access FreedomBox using URL https://freedombox/plinth
3. The access failed on Firefox but not Chrome

Two questions:

1. Is this a problem that our development can solve, or is it an issue caused by Firefox?
2. If it cannot be solved by our development, how should we communicate this issue to users in our documentation?