Well this shit is just creepy
I guess theoretically this may allow sites to theme in line with this preference, which (eventually) might negate the need for add-ons like Dark Background and Light Text.
Fewer add-ons = better.
Unfortunately, more fingerprinting = worse.
I am a sucker for dark mode… and I agree, that this could be a convenience.
Isn’t it always the decision go with privacy or convenience.
That’s kinda strange, but I do love that dark mode…
The first problem I thought of was not all sites implementing support, so I’ll be lulled into a much higher brightness than I’d normally use, and then I’ll open a site that doesn’t support it and sear my retinas or something 
So I don’t think it’s super useful.
it’s good you know ? i mean for developers it’s will be good, like firefox & battery API right ? but problem that some developers make bad scripts to spy on you so yeah (problem not in the new settings problem in developers)