Hide My Browser Free is an entirely free utility to hide the windows.
You can easily display or hide the windows of browsers with a keystroke or with a mouse click from the tool bar: hide the windows of Internet Explorer, Mozilla, Firefox, Opera, Netscape, etc. It is possible to hide quickly the windows so that nobody can see what you are doing. Then, in order to display them again, simply use hotkeys.
Hide My Browser Free can be downloaded free of charge from this site and runs on Windows 95 and higher.