How can I stop being a self-righteous jerk?

I have always considered myself a nice, honest, compassionate person, but I always have a problem with being a self righteous jerk. For some reason I can't control this. One time when I was at a job and the company was losing money instead of doing the right moral thing and admitting they were losing money (mostly to an ineffective business model that is doomed to fail anyway) they pulled people in and blamed them for the job performance which was CLEARLY A LIE!!!! I knew that I was doing a superior job when they lied and let me go. When that happened i turned self righteous. I insulted my bosses character flaws, attacked him personally, and threw in his face all of my education and career accomplishments that he doesn't have. He got fired a month later by his boss.

I regret saying all of those mean terrible things and wish I could take them back. When I look back I realized that I BECAME THE BIGGER JERK THAN HIM and he didn't deserve any of the things that I said to him. I know what I said really hurt him and I wish I could say I was sorry but he got fired so I can't. How do I fix this.