Problem initializing designMode on DOM-generated element

I'm having problems getting an IFRAME into designMode in Gecko. It works fine if the element is hard-coded into the HTML, but if I create it via DOM scripting, I get the following error

Error: uncaught exception: [Exception... "Component returned failure code: 0x80004005 (NS_ERROR_FAILURE) [nsIDOMNSHTMLDocument.designMode]" nsresult: "0x80004005 (NS_ERROR_FAILURE)" location: "JS frame :: file:///C:/work/peterbailey.net/test/rte/new/js/GildedRTE.js :: enableDesignMode :: line 33" data: no]
I've tried both document.createElement and document.createElementNS to creame the IFRAME, both cause the error. Here's how I'm attempting to turn designMode on
function enableDesignMode( id )
{
var iframe = document.getElementById( id );
if ( iframe.contentDocument )
{
iframe.contentDocument.designMode = "on"; // This is line 33 that the error mentions
}
else
{
iframe.document.designMode = "On";
}
}
Like I said, this function works on hard-coded IFRAME elements.

Any clues?

UPDATE

I was forgetting setAttributeNS too. Now that I've done that, it turns designMode on (I can type in the IFRAME) but it still throws the exact same error.

:confused:

Do I just need to toss an innocuous try...catch around it to avoid the error?

UPDATE to the UPDATE

Using the try...catch works, but something is still amiss. When comparing the effects of the enableDesignMode function on my DOM-generated IFRAMEto a hard-coded IFRAME, there are some discrepancies.

For example: none of the navigation keys work (Home, End, PgUp, PgDown, all four arrows) in the DOM-generated IFRAME. Neither do Insert or Delete.

:confused: :confused:

http://bugzilla.mozilla.org/show_bug.cgi?id=191994

Seems related.

I got it fixed. I needed to add a timeout to give the operation some "breathing room" or something.

setTimeout( function() { iframe.contentDocument.designMode = "on"; }, 10 );