I found my firewall was turned off inadvertently. Is there any way of putting the Windows Firewall icon into the system tray where it will show on and off? I have managed to put Windows Defender there and feel there must (or should) be a way to do this.

What operating system are you running?

Sorry, Windows Vista at present though plan to change to Windows 7 sometime soon.

There's no way that I know of to make Windows display a firewall icon in the system tray. However, the Security Centre will give alerts when it detects that something has been turned off or isn't working properly. I don't have Vista or XP so can't look at this myself but I can give this link that describes how to enable or disable alerts from the Security Centre:

http://www.mydigitallife.info/2007/03/18/disable-security-center-alerts-in-windows-xp-and-vista/

Third-party programs take over security measures when installed and Windows own firewall normally gets disabled. This means no alerts from the Windows Security Centre regarding the firewall not working. The status of the firewall is then given by the look of the third-party program's own icon (a cross through it when the firewall is disabled for instance).