Basta adicionar XMonad.Hooks.EwmhDesktops.fullscreenEventHook à sua definição de handleEventHook. Aqui está um trecho da minha configuração
import XMonad.Hooks.EwmhDesktops
main = do
xmonad $ docks $ ewmh def {
handleEventHook = handleEventHook def <+> XMonad.Hooks.EwmhDesktops.fullscreenEventHook,
modMask = mod4Mask,
terminal = "terminator",
workspaces = myWorkspaces,
layoutHook = myLayoutHook,
manageHook = manageSpawn <+> myManageHook <+> manageHook def,
borderWidth = 1,
normalBorderColor = black,
focusedBorderColor = yellow,
focusFollowsMouse = False,
logHook = dynamicLogWithPP xmobarPP {
ppOutput = hPutStrLn xmproc,
ppTitle = xmobarColor "green" "" . shorten 50}
}'additionalKeys'