Firefox and LibreWolf were part of the update when I updated this morning. Now, when saving an image or file from either browser, the dialog box looks like outdated Gnome/Adwaita. This happens in my primary EOS user account and my clean troubleshooting EOS user account. Seems only Firefox and LibreWolf are affected…
Check if the value of widget.use-xdg-desktop-portal.file-picker reverted in about:config
It should be 1 for the KDE file picker, might require restarting browser afterwards.