My preference is nearly a dark cave and people think I'm odd. I also use a plugin to make FF have dark backgrounds and light text. I don't enjoy squinting all the time.
In at least one case, it wasn't just me. I used to work editing photos on California's central coast and after we moved to a building with loads and loads of skylights, and got a bunch of new glossy-screen iMacs, it was really hard to get color accuracy if you wore anything but a black or white shirt. It was like staring at a mirror all day long. Eventually we got umbrellas to blot out the sun and that helped.
I have just been using stylus and using dark themes for sites I use often, but would love a more automated approach, especially for sites I don't use that often.
You may be the minority at least, but you also have to see it as having options. There's a big difference between having a room with a window and opting to close the curtains, and have no window at all. Most likely you also don't get depressed by working in a bright room, while others actually suffer if they have to little light.
I would guess that all Scandinavia countries have similar rules, and there's actually a minimum amount of light you're legally allowed to have in a room. The law in Denmark for instance actually require a room to be insanely bright.
Our office recently installed dimmers on all the lights and if you walk around, every single group has it set to the lowest it'll go. We also have our blinds down - they darken, but are semi transparent, so you can see outside, but it cuts the light by a ton.
I wonder if it is related to coming from a northern country (Scandinavia) where ~1/4 of the year is really dark.