User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:66.0) Gecko/20100101 Firefox/66.0
Steps to reproduce:
On a touchscreen laptop using Arch Linux / Gnome 3.30 / Wayland, start Firefox with MOZ_USE_XINPUT2=1 (without which no touch events work). From Menu > Customize, uncheck "Titlebars" to switch to client-side decorations.
Using the touch screen, touch an empty spot on the titlebar and drag.
The window did not move.
The window should move as when dragging using a mouse or touch-dragging with system titlebars.