Firefox, thumbnail on hover

Hi all,

Firefox shows a thumbnail on hover when the titlebar is activated (on Firefox). Right.

When the titlebar is deactivated, if I want a thumbnail to appear, Firefox has to be maximized. It works no matter if Firefox is on the desktop or maximized and then reduced in the list of windows. If Firefox is not maximized, the behaviour is as if I had checked "Hide thumbnails on hover".

Using 20.04