Until very recently, McDonald's fries were cooked with 93% beef tallow -- their fries had more saturated fat than a hamburger!
Due to some bad publicity regarding the amount of cholesterol in their fries, they switched to vegetable oil in 1990. However, McDonald's still continues to use an ingredient they refer to as "natural flavoring," which they admit comes from an animal (they just won't reveal which one).
So, you can still get beef from McFries? Oh, ok. Trace amounts... yea. OMG MY FRIES ARE MADE OF BEEF!
As far as the whole cleanliness argument... that applies to any restaurant.