It is because that is a GTK file dialog.
If you want to use a KDE file dialog with Firefox you can.
Set GTK_USE_PORTAL=1 and install xdg-desktop-portal-kde
It is because that is a GTK file dialog.
If you want to use a KDE file dialog with Firefox you can.
Set GTK_USE_PORTAL=1 and install xdg-desktop-portal-kde