I was working and made a small mistake at work, my manager started laughing and calling me a retard to other staff. I walked off the job and now they want to fire me. Can they do this?

I would recommend making a formal complaint to the company's HR department regarding the workplace harassment you may have been subjected to by your Manager. You should also review the Severance Pay Calculator to determine your entitlements in the event your employer terminates your employment and contact us to speak with a lawyer.