Different behavior on FF v Chrome

var dialog = this,
data = {},
heading = editor.document.createElement( 'div' ),            
expand = editor.document.createElement('div');
this.commitContent( data );
 heading.setHtml(data.header);               
expand.setHtml(data.expand);
editor.insertElement(heading);
editor.insertElement(expand);

The output on FF:

<div>title</div>

<div>expand</div>
<p>&nbsp;</p>

The output on Chrome:

<div>title
<div>expand
</div></div>
<p>&nbsp;</p>

In chrome, the 2nd div is within the 1st div while in FF,IE the 1st and 2nd div are separate.
Also why does an extra <p> </p> get added at the end?