Confirms this browser can reach the STUN servers Sharpen's voice uses, and finds the firewall and NAT conditions that break calls.
Heads up. This is a snapshot of one moment on one machine. A VPN, virtual desktop,
Wi-Fi, or a corporate proxy can all change the result, and it may differ at another time of
day. Treat it as a starting point, not proof that the network was or was not the cause.