Window World is very lucky that there was nothing under my window when it fell to the floor -- like a table, or a cat, or a child! The window was replaced, with the representative telling me, "If the window is not closed properly, it will fall out." I would say this is a serious design flaw.
This is the most serious but not the only problem with the installation of my 11 windows. Be sure to ask about how the top window can "slip" down if the windows aren't locked.
Window World has replaced 66 windows in my building to date. Our other residents have been informed of this problem, so I doubt it will be replacing more windows in the future.
Reason of review: Bad quality.
Preferred solution: Let the company propose a solution.