There are browser addons which will copy the text automatically so you can retrieve it later.

For Firefox I recommend TextArea Cache Lite (which replaces TextArea Cache which will cease to work in Firefox 57). It's not perfect but it works with Mudcat.

I don't use Chrome but I know of Lazarus and Tire I don't know if these work with Mudcat, but I expect so.

My own Mudcat Browser Tools (qv) addon saves the post automatically too, but those addons work with more sites, and save the text even as you're still typing it.