I would first suggest starting a journal. Start tracking what you do at work, all of your accomplishments, all of your projects and contributions then also document all of your interactions with your boss, remember to document dates and circumstances around each entry.
You need to do this for a couple of reasons. First if you work for a larger company you can take this to HR (or your bosses boss) and show them that you are a valuable member of the team and you are wrongfully being singled out also if you are fired you'll need this to build a case for unemployment or for a wrongful termination claim.
I'd also work on getting your resume in order and start networking. Maybe join linkedin.com to make connections that may be helpful in seeking employment elsewhere. Even if you're not fired now or in the near future I'd get out there and start looking for a new job ASAP anyway! It's a very competitive job market, doesn't hurt to start sooner then later.
