Due to an eyesight problem I run everything on dark background including theme, editors and web. I'm not sure if this makes me sleepy, but it is possible to try it. The best firefox addon for dark browsing is > https://addons.mozilla.org/en-US/firefox/addon/dark-backgrou...
I've been doing the dark backgrounds for years, due to being farsighted. I recently switched to a high-contrast theme, and it is way easier on the eyes. I think not all dark themes are equal when it comes to amount of work the eye muscles have to do.
I see, kinda ;) I musn't grumble about my condition, just thought it relevant that its quite possible to try working in a dark background to see if it affects sleep cycle.