Use contenteditable instead of designMode

This fixes an obscure problem in Firefox with iframes.  JavaScript is enabled
inside the iframe initially.  However, if the iframe redirects to a different
page, JavaScript is then disabled.

Leaving designMode off fixes this problem.
Try setting contenteditable indefinitely

Instead of only 3 attempts.  3 is not enough if the WYSIWYG loads slowly.

Not really sure why this only tries a limited number of times.  It's crucial
that designMode/contenteditable gets set, otherwise the WYSIWYG doesn't function
at all.