In the firewall section of the options dialog, the 'Firewall support' combo box initially has 3 options; None, Server, DCC. When I select one of the latter 2, it changes the combo box to show; Server, DCC, Both. The 'None' option has gone, thus making it impossible to disable the firewall through the options dialog. I have to use the '/firewall off' command instead.
Bug discovered on mIRC 6.03