Disable client-side decorations in "Save as..." dialog?

I’m not sure if this is a change in Firefox itself or the result of something I did (it happened around the same time I switched to plasma6 and wayland), but very recently Firefox started using Client-Side Decorations (CSD) in the “Save as…” dialog. Meaning it now puts the “Cancel” and “Save” buttons in the title bar.

This is not ideal for me as nothing else on my system uses CSD. As a result the dialog is very awkward to use and does not fit well with the rest of my environment. The old dialog was perfect, and I’d want it back.

It there any way Client-Side Decorations can be disabled in the “Save as…” dialog?