Code:

window.localStorage&&$(function(){
$(function(){
if($("#text_editor_textarea").length&&typeof $.sceditor!="undefined"){
var a=$(document.post.mode).val(),
d=$("#text_editor_textarea").sceditor("instance"),
e,f,g=function(){
localStorage.setItem(a,d.val());
f=0},
b=JSON.parse(localStorage.getItem("br-data"))||[],c;
switch(a){
case"editpost":return;
case"reply":a+=$(document.post.t).val();
break;
case"newtopic":a+=$(document.post.f).val()
}
a=parseInt((my_getcookie("fa_"+location.hostname.replace(/\./g,"_")+"_data")||"0").replace(/.*s:6:"userid";(i:([0-9]+)|s:[0-9]+:"([0-9]+)");.*/,"$2$3"))+a;
-1!=(c=$.inArray(a,b))&&b.splice(c,1);
if(20<b.length){
for(c=b.length-1;0<=c;c--)/^\s*$/.test(localStorage.getItem(b[c])||"")&&(localStorage.removeItem(b[c]),
b.splice(c,1));
20<b.length&&(localStorage.removeItem(b[0]),
b.splice(0,1))}b.push(a);
localStorage.setItem("br-data",JSON.stringify(b));
$(document.post).submit(function(){
localStorage.setItem("br-target",a)
});
!d.val()&&((e=localStorage.getItem(a))&&d.val(e));
d.keyUp(function(){
f||(f=setTimeout(g,3E3))
})}})});
window.localStorage&&(localStorage.getItem("br-target")&&function(){
$("meta[http-equiv='refresh'][content]:first").length&&function(){
var a=JSON.parse(localStorage.getItem("br-data")),
b=localStorage.getItem("br-target"),c;
if(-1!=(c=$.inArray(b,a)))a.splice(c,1),
localStorage.setItem("br-data",JSON.stringify(a));
localStorage.removeItem(b)}();
localStorage.removeItem("br-target")}());

Additional Comments and Instructions Following Code in Originating pm wrote:Enter the admin panel, head to the "Modules" tab.
Scroll to the bottom, should be a section titled "HTML & JAVASCRIPT"
Click the link that says Javascript Codes Management
Create a New Javascript
Name it something conspicuous like "KH AUTOSAVE POST THINGY" or what have you
Paste the code into the area below

Save, and you should be golden. To know it it worked, the topic will create a URL. It'll be right after the name. If you click the tiny screen after it, it'll take you to page like this one:
http://genesisproject.forumotion.com/10294.js