I've lost jobs behind just that. But I was being pretty excessive. I've got a pretty addictive and obsessive sort of personality.
The thing about owning a business is the business owner gets to decide what is or isn't okay. Lots of time business owners don't get the respect they deserve. People have no idea, and often just don't care how many hours a business owner has to put into keeping a business running. Never mind the hours or years of planning and saving they may have invested in getting a business started in the first place.
My opinion is that employees thinking they can dictate what can or can't be done on the job are tails trying to wag dogs. But I'm also a recluse, and I have not had an honest job in years. Were I wealthier and wiser I'd have a business, and I'd let performing employees look at Facebook or whatever so long as they kept performing.