While I can certainly understand why you would want to do it, let me ask you a question first: Will it change your situation, or get your job back, or get a new job for you, or pay any bills? Will it do anything constructive at all?
It won't educate him or make him behave differently in the future. He knew that you had a family when he fired you. All managers know the impact on lives when they fire someone, and terminating a position is one of the most dreaded parts of management.
Even if you don't need a reference from him, you'll find that this is a small world, and you might cross paths with him--or with someone he knows--another time. I left one company to go where I thought no one would know me, and found several former co-workers there. One of my former co-workers--who I often clashed with--joined the same company a few months later, and then I was promoted to be his boss. Now I own my own agency, and I have clients who were former peers, direct reports, or co-workers. It's a small world.
Send an e-mail won't even ease your emotional pain. I understand that you are hurting inside just as much as you are hurting financially. By firing you to make room for someone else, he said that he values you less than the other person. He doesn't even seem to care. Saying these things out loud (or writing them on Yahoo! Answers) is a good start to the emotional healing process, but you'll need to go further. Always remember that he can only make judgements about your WORK, not about YOU. YOU are NOT your WORK.
You have an intrinsic value that he can't change. That intrinsic value is what your your husband, kids, and friends see, and that's why they love you so much. When you come to grips with that, and learn to put the previous job behind you, then you'll be able to let that intrinsic value shine more brightly, and you'll be able to move on to a new job. It is a long and difficult process, but it's the only way to heal. Sending an e-mail to him is like picking at the scab, which PREVENTS healing.
I wish you the best as you move forward, and you and your family will be in my thoughts and prayers.