This is very easy to reproduce: Start Wayland session Start firefox Sart Konsole Close Konsole with keyboard sequence CTRL-D Firefox will ask you to bookmark the currently active webpage because the keyboard sequence to close Konsole gets not consumed but propagated to Firefox. This is true for other keyboard sequences as well, eg. Open Firefox Open Emacs Close Emacs with ALT-F4 Firefox will show the menu bar which is shown when pressing the ALT modifier
This is a bug in XWayland which is fixed in latest Xwayland release. I just tried to reproduce and the problem does not exist on my system which has an up to date XWayland.