Olli 1978 wrote:
What is helping for me a little bit is the "Stylish-Plugin" for for Firefox.
Ok, it doesn't help for Excel, Word and so on, but at least all the websites and intranets on my work are now dark with light text ;-)
Just google for it, it is really easy.

I use a similar plugin called PrefBar, it gives you a toolbar so you can click between a darkened theme and a normal theme.  For the rest of Windows I use the Hi Contrast Colour Scheme (purple one) and it works well enough, although there are bits of software out there that don't support it at all.