>> I'm using handleEventHook = fullscreenEventHook
>> from XMonad.Hooks.EwmhDesktops as otherwise pressing 'f'
>> in mupdf doesn't make it fullscreen.
>> Unsuccessfully tried fullscreenEventHook from XMonad.Layout.Fullscreen.
>
> Note that merely using the fullscreenEventHook from that module isn't
> enough. This hook merely enables the layout modifiers in the module to work.
> To get the behaviour you want, add the event hook and the manage hook from
> the module, and add the fullcsreenFull layout modifier to your layout hook.
> See also the module documentation[1].
>
> [1]:
> http://xmonad.org/xmonad-docs/xmonad-contrib/XMonad-Layout-Fullscreen.html

I tried to make that works but failed.

It seems that both XMonad.Hooks.EwmhDesktops XMonad.Layout.Fullscreen
provide the same hooks and that it results in a compile error
if I try "eventHook = fullscreenEventHook"