Doubleclick the window title- or bottom bar to maximize the window. Try to change the browser size. Doubleclick again to restore the former size.
Check also the behavior of minimzed windows, which are in maximized mode (click on minimize icon, afterwards doubleclick the bar).

Use the API function WinLIKE.maxvals in the BODY onLoad event to limit the maximum size (in this case no limit (=100%)) of maximized windows. See the source code of this file for a sample.

To disable this feature, set the property .Siz (sizable) to false.