A darker Firefox

With all the rage that is being going on with dark themes, for instance: 10 Beautiful Themes for Ubuntu Intrepid Ibex, one things I really hate about using them, is that the default website looks like a window onto a totally different planet, most of them are white.

That was the main reason I haven't settle for a darker theme until now, but, by pure chance I found out that pressing the key combo Windows + n, you turn onto a negative the whole Firefox window.
The problem, of course, is that all the images on the window show up as a negative too... (I'm thinking on a way of dealing with that...)