A standard behavior of any application on Ubuntu is when you mouse middle button click on any open window top title bar that application window gets lowered to underneath all other open windows ... This has worked fine on ff nightly until a few days ago ... this is even when ff setting -> Customize -> Toolbars -> Menu Bar it enabled ff nightly 82.0a1 (2020-09-08) (64-bit) on Ubuntu 20.04 As a long time ff user on nightly while on various releases of Ubuntu over the years this typically works OK however about once a year it stops working then somehow starts working OK On same Ubuntu 20.04 machine all other applications are OK with this behavior