Firefox/LibreWolf window outline and shadows conflict with Niri borders

[1seco]

I would love to have a clean setup with my own choice of color and border width but (as far as I see) only librewolf's windows have a tiny iris border and a colored shadow which looks really out of place.

pcmanfm for example behaves correctly with no border or window shadow. It seems that librewolf/firefox-based browsers are the problem here, and I need help either completely disabling borders and window shadows, or having the possibility of easy customization in the future.

Also, the Gradience link in the readme is dead and it's going to be a hassle to install on Void.

The above is not my border config. I have all borders disabled. I have tried come gtk configs in the few forums that mirror my issue, but most of them might be either outdated or gtk-3 only and do not work.