I have a new PC running Kubuntu 22.04, with Mozilla Firefox 120.0.1 (64 bit) installed. Standard, the system window title bar was hidden. But I wanted access to the "Move to desktop" menu and wanted the title in the title bar. So, in "Customize toolbar" I checked "Title bar". The title bar reappeared, but a complete border along the Firefox window became inaccessible, and when clicking in that zone, it effectively clicked in the window behind. In particular, the complete menu bar is inaccessible, as well as the scroll bar on the left and in the bookmarks sidebar the fold/unfold. And Mozilla Thunderbird 115.5.0 has the same annoying behaviour. Even when hovering over some menus in the Mozilla window, you can sometimes see reactions from the window under the Mozilla window. On older Kubuntu computers (up to 18.04) with older versions of Firefox (up to 113.0.2) and Thunderbird (up to 102.11.0) I do not have that problem. How can I get at the same time access to both the system title bar and the menu bar ?