Line breaks

In edit mode, when the Enter key is pressed:

 Internet Explorer inserts: <p> </p>
 Mozilla/Firefox inserts: <br />

When shift-Enter is pressed:

 both Internet Explorer and Mozilla/Firefox insert: <br />

htmlArea is trying to compensate for these different behaviors:

 htmlArea intercepts the Mozilla/Firefox Enter key event
 htmlArea wraps the br tag in a pair of p tags: <p><br /></p>
 on submit or on toggle to textmode, htmlArea strips the br tag.

htmlArea then inserts a non-breaking space in any empty text node or one that contains only spaces.

 When the text node is edited, the non-breaking space is replaced by a normal space.

The net result is the same in both Mozilla/Firefox and Internet Explorer.