This add-on for me:
1. Complementary to Dark Reader.
2. Easy to switch on or off. (Plus) There is only a single button in the menu. No option pages.
3. May omit some pictures. (Minus)

While this addon works very well initially, when I navigate to the next chapter on https://tiraas.net/2016/05/30/10-35/ it frequently fails, so I have to disable it and re-enable it. (not every time, but more than half the time I'd say.) It might be something to do with a timeout or a late load of a stylesheet on that page. (I'm on Firefox for Android)

Great consistent colors across all sites! Shame it doesn't work with the vim-vixen addon though.

Just what I was looking for. Simple one click toggle, works well on mobile. The black it makes the background is usually pure black, which looks great on AMOLED phones.

Fails in weird ways on some sites, but it's easy enough to simply turn it back off again on those sites.

Work pretty well, would be even better if it could be activated per tab!