I have firefox 67 install on f30 and its not honouring the prefers-color-scheme CCS media query.

I raise https://bugzilla.redhat.com/show_bug.cgi?id=1716134 but no useful feedback yet. It explains how to check the CCS medai query.

I use KDE in dark mode by using the Breeze Dark theme.

I was told that the problem might be a bug in the Breeze Dark theme if it does not set the "dark mode" in the right way.

Barry