The funny thing, is that it doesn't matter if he fired them for clicking "like" on facebook, Virginia is an "At will" employment state. Because the like button had no legal precedence to be protected speech when they were fired, the sheriff was not in the wrong.
Heck he could have fired them for voting for Obama, being gay, being strait, being too fat, thin, tall, short, having an ugly face, etc...
Race, Religion, Gender, Age, Military status, or disabled status are the only protected ones for discrimination. In an "at will" state you can be fired for anything other than those 6 items.