I got fired from my job of ten years. I enjoyed a excellent relationship with my boss until the last couple of years of being there. My hard, honest work spoke for itself, as I am not a minion, and I was always praised for keeping to myself, and never causing problems at work.
Things seemed to change after this youngster, fresh out of school, was hired and started to aggressively brownnose boss-lady.
She and another trouble-maker started going to her about silly things that supposedly I did. (This other trouble-maker is a BULLY and my boss is TERRIFIED of her. She also has a close, personal relationship with someone in administration.) Meanwhile, another one of her schoolmates was hired, so she had even MORE back up.
I'm not saying I was perfect, but I started getting written up for menial things, and I KNOW for a fact it was things that EVERYBODY did on a DAILY basis! I tried to explain to my boss that others were doing it too and that just got me into more trouble!
In fact, this little groveler, BLATENTLY posted something negative, which was totally untrue, about another co-worker on a very popular social website. Nothing was done to discipline her. People get terminated for that, don't they?
So in the end, I got fired. A nice lady I worked with there called me later that day to tell me that one of the flatterer's friends was hired AS SOON AS I LEFT!! Boss-lady called her to tell her she got a full time job. Hmm.
My job is extremely specialized in the medical field. Everybody knows each other,
And I'm afraid that when I go out to look for a new job, my ex-boss and these not nice people will start saying negative things about me.

Were you fired with just cause? Laid off? Let go without reason?
If they had a just cause to fire you, then you need to come to terms with what you did that was wrong. When your boss confronted you with what you did wrong, she wanted to know that you realized you made a mistake and it would not happen again. By telling her that it wasn't wrong because everyone else does it too, you showed that you had no remorse for what you did and no respect for the rules. I have been in a similar situation and was fired for it as well. The best thing to do is find a way to turn this negative into a positive, learn from your mistakes, and move on.

If I am way off base here and you were simply laid-off then you should have no problem finding new employment in your "extremely specialized" field. (hopefully with a better work environment)

If I am way off base here and you were let go without reason, then maybe you should be having a conversation with a lawyer.

And your question ? Life is tough, company politics work this way, you are on top, they are on top and you get kicked to the curb. Hopefully you kept copies of annual or quarterly reviews. And for reference you also give other people you worked with