Explayando más lo que te comenté antes
Cita: Actually, this has nothing to do with case sensitivity. This is a security feature. The functionality of :visited pseudoclass has been restricted in many modern browsers (Fx4, IE9, Chrome) to prevent CSS exploit: read about it ....
Detalles:
http://hacks.mozilla.org/2010/03/pri...-css-vistited/
El unico navegador que te permite la modificación es Opera
SAludos