Comment by LargoLasskhyfv

> The idea that I need to have window decorations and the “GTK window decorations” configured separately is just …

Yah, well, I'm on Plasma/KDE and that idea enables me to close apps by throwing my mouse on the right top corner and clicking on that [X] there.

After having disabled the titlebar in FF itself once in "Customize Toolbar". It's the leftmost box on the underside, just uncheck it.

Not even in the settings Plasma/KDE has for that, too. There only "maximize" is activated.