In the Tools User Setup Files page, you can set a limit for the number of read-only windows open at one time. When you reach this number, opening a new read-only window closes the least recently used window. Scientific Notebook is a multiple document interface (MDI) application, while the standard browsers are single document interface (SDI) applications. In an MDI application, you want to control read/write windows yourself. At the same time, you may want several read-only windows open at one time.