How do I undo erasing a message I was typing on Facebook?

I was on my Facebook replying a message today when I pressed some random button on the keyboard that caused me to click who knows what in the toolbar or something, making me go back to the previous page before I began my message. I had almost 3 long paragraphs written & I want to know if there is any way to retrieve what I wrote with some Firefox add-on/app, or something on Facebook? I do not want to re-write everything I wrote again. I would simply like to find a way to make it all be retrieved. If there is no way though, I will force myself to start over.