I can reliably reproduce the issue in a VM running 18.04 with firefox 62.0+build2-0ubuntu0.18.04.5. This affects only the default X session, the issue cannot be observed under wayland.
I can reliably reproduce the issue in a VM running 18.04 with firefox 62.0+build2- 0ubuntu0. 18.04.5.
This affects only the default X session, the issue cannot be observed under wayland.