This is a common request regarding the GUI. Unfortunately, it is part of the Windows MDI interface and cannot be changed by an application. Microsoft decided not to update the MDI interface (where windows are contained within the main window in an application) in newer version of windows because they are moving away from MDI to SDI. SDI is like Firefox, where windows are maximized all the time inside the application, so all you can see is one window at a time. mIRC can already do SDI - all you have to do is to maximize the windows inside mIRC. While I could turn mIRC into an SDI application permanently, most users find MDI, with multiple visible windows, useful, so this is not likely to be changed.
