Visit Moustachemedia.com in IE, they don't let you view their site, I bet a lot of their potential clients use IE and they just turn them away, seems like they don't want the business. Although I use and recommend Firefox, I develop sites that work in IE, Firefox, Safari and Chrome, 

Maybe they can't be bothered to do any cross browser testing, or perhaps they don't have the ability to get the sites they write to look good in IE, it would certainly put me off using them.