My thought is keep looking, look into OS settings. Mac or PC? Probably under Font related settings, could be under Accessibility, could be under Display/Monitor. Looks to me like some kind of text sharpening, anti-aliasing, "TrueText", "ClearText", "SharpText", or other feature like that is either turned ON or OFF, not the way you're used to. Could be wrong, just a guess-idea to check around for. Since you already checked browser-zoom.