I was recently on short term disability for severe depression. Mental and emotional instability. After four months I returned yesterday and was presented with a post I put on Facebook in September. Two months ago. It did bash the company I worked for. I was upset and in a bad place. I have everything legally documented. Is this wrongful dismissal? Isn't this discrimination?

If you have a doctor that would be willing to say that when you posted those comments you weren't "in your right mind" and that you did it because of a medical condition, then it is absolutely a wrongful dismissal. If a doctor is not willing to say that, then bashing the company online would be cause for dismissal. If you have the backing up of a doctor, please give me a call to discuss.
Lior Samfiru