Be aware though that this will make firefox tell sites that you want a light color scheme instead of doing the more sensible thing and indicating no preference.
Though IIRC from some bugginess I was noticing a while ago, only to the JS API, it will still obey the dark color scheme media query (but sometimes inconsistently, I would load the same page in multiple tabs and sometimes get dark or light schemes).
This chain of replies containing only pertinent facts to inform the reader exemplifies what's so great about Hacker News. :-)
Interesting. I’m a light mode user, so hadn’t seen that.