I strongly disagree with this step. Ensure your performance is exceptional, flawless, and that everyone sees it. It's hard to do, hard to keep focus and not slip when everyone else is misbehaving, but it pays off:
1) It keeps your hands clean. Others won't know the inside story of why you were let go; if they see you slacking, they will doubt your character and work ethic and believe it's your fault. If they see exceptional performance they may give you the benefit of the doubt. You want them wondering, 'how could they fire him/her?'
2) It leaves a strong impression with everyone, possibly even your boss, of your work ethic and professionalism: 'Even knowing he/she would be fired, look what he/she did'. A crisis is a chance to show your quality.
3) It keeps your hands clean, which means you can sleep easily in the future. Don't do anything you will question later. Be proud of what you did and that you rose above your manager and the situation. Having been in similar situations, it made a great deal of difference in my self-respect and peace of mind down the road.