I'd be very cautious with plain ol' window screens and any cat, especially an F1! We have either pet proof screen (on our screen doors) or wire mesh guards on all of our windows. I have had "regular cats" claw out typical screening and escape years ago, and now that we have newer vinyl windows vs our old wooden screen/window combos, I am doubly vigilant on window safety. Our newer screens are attached via a squeeze clip, so easily popped out, and did once have a cat lying in the opened window and accidentally pushed the screen out and open when she rolled over, so we now have the screen guards on all of them, ugly and institutional as they may be. I did use the wooden screen sliding screen inserts in the past, but have since heard they are not as safe as I once thought. I find my window guards through a variety of sources (depending on the window size) including our local hardware stores and thrift shops. For our smaller windows, such as in our bathroom and back laundry room, I use the grid panels from wire shelving units. The window opens top to bottom and I secure the panel under the upper window lip and drop the top window part down tight. There is enough weight to the top window to keep it secure when opened so far, but I do check them constantly to be sure no one is messing with them and trying to escape.