ASK - requirement to access web tunnel

hi there,

currently I'm trying web tunnel for vpn ssl.

I notice, outside can access vpn ssl portal over web browser, without installing forticlient.

my question is:

1. what is the requirement on client side, to run web portal / web tunnel, by web browser?

trying with firefox, edge, chrome. it always stuck after enter login info, show error message :

"The SSL-VPN host-check Java applet cannot be loaded. Please check that you have Java installed and enabled."

2. if in the future, I want to disable this feature, so outside only can reach via forticlient and tunnell mode only.

how to that?

need advice and guidance. thank you.