A few years back I wrote a small script that prevented you from trying to make a post on the forum when you've idled out (and thus losing your post). I've made some adjustments to it, it now works for both the forum and the post office, and it will also show older posts (in reversed order, latest first) on the editing page.
http://pasteboard.co/vnT7ChM.png
http://userscripts.org/scripts/show/109685