Firefox does not always follow the system proxy, so it can show no connection while other apps work normally.
If you use TUN mode (VilaNet's default on most platforms)
Nothing to configure — all traffic including Firefox goes through the tunnel.
If you use Proxy mode (desktop)
- Open Firefox and go to Settings (older versions call it Options).
- Search for proxy, then open Network Settings → Settings…
- Choose Use system proxy settings and click OK.
If you prefer to set it manually, choose Manual proxy configuration and enter SOCKS host 127.0.0.1, port 10081 (SOCKS5). You can confirm the exact address in VilaNet under Settings → Local Proxy.
An illustrated walkthrough is also available: https://vilavpn.com/f.pdf (screenshots show an older Firefox layout; the steps are unchanged).