Here is the mozilla version I am running:
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.6) Gecko/20040113
I also tried Firefox:
Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.6) Gecko/20040206 Firefox/0.8
The content in the example is held in an editable document in an iframe. So I tried this:
this.iframe.style.display = "none";
this.iframe.style.display = "block";
//set it back to designMode
This does fix the rendering problem, however you can see the content quickly jump from scrambled to formatted correctly.
I'm downloading mozilla 1.7rc to give it a go.
Well, 1.7rc does it as well.