Xwayland window resizing is very ugly (black flicker in place of drop shadow)
Running e.g. Thunderbird or Firefox via Xwayland, when resizing any of their windows, one can intermittently see ugly black flickering in place of the drop shadow around the window.
This can also happen when they open a new window, e.g. a dialogue, but it's more noticeable when resizing. It also happens with other apps via Xwayland.
I was assuming this was an Xwayland issue and needs to be addressed there, see e.g. https://gitlab.freedesktop.org/xorg/xserver/issues/636 . However, today I realized this doesn't happen with weston, so mutter seems to at least play a part in it. In fact, since the drop shadows are drawn by mutter itself, it should be able to prevent these artifacts from appearing?