Переопределить цвет фона в Firefox ⇐ Html

[Anonymous]

I want to change background color in Firefox from white to gray (because my eyes get tired of white)
I try to change it this way:
Preferences -> Language and appearance -> Font -> Colors
But it does not work as expected on some complex web sites:
Original page:

Страница с цветом фона изменил:


Подробнее здесь: https://stackoverflow.com/questions/699 ... in-firefox