Comment 2 for bug 731643

There is a link to the plugin mentioned by Jono at https://www.tinymce.com/docs/plugins/autosave/

If you enable the plugin it will record your input every 30 secs (or specified time) to local storage or session storage and there is a restore draft button added allowing you to restore the information or you can set a variable to allow it to restore automatically on page load

Here's a demo of the TinyMCE autosave plugin: http://valtlfelipe.github.io/TinyMCE-LocalAutoSave/

There are two types of webstorage for html5, one is sessionStorage and the other is localStorage. The localStorage object stores the data with no expiration date. The data will not be deleted when the browser is closed. SessionStorage is not recommended in your case because everything would be gone when the session is lost, i.e. a timeout occurs.