Windows with Firefox: Firefox extension AnyColor tweaks the look of Firefox on they fly, letting you choose custom colours for every pixel of the Firefox chrome. Everything from background and text colour to header and footer images are customizable, meaning you can easily tweak the look of your Firefox window without so much as restarting. The extension comes loaded with several presets, like the Dark theme pictured (which, incidentally, is really easy on the eyes). AnyColor is free, currently works in Windows only. It's also an experimental extension, so you might want to back up your profile before trying it out. If AnyColor isn't quite for you but easy Firefox theming is, check out previously mentioned Personas.