Teenager fired for commenting on Facebook at work about how she was bored at work

Yes, but you are not suppose to admit it.
If you are "bored" and work, then your performance goes down. And if your manager knows that, then the logical thing to do is replace you with someone whose performance is better.

That might not be the case for manual work, but for jobs that require mental ability, level of boredness is more important.

So you don't have to have fun, but you can't be bored. lol

Or better yet, don't type stuff about your work on Facebook.

Keep your personal and work life separate (unless you are banging your boss or co-worker. Then it is harder to keep them apart).