Is there a known gotcha?

Working on Ext JS 4.2.2 app (Sencha Architect 3.0.1) using Ext Direct and it works fine in Chrome. Most things (including forms and remote calls using Ext Direct) work in Firefox (tried Linux, Windows), but that one form with Ext Direct file upload doesn't.

No request seems to be sent: No request seen in Firebug, no request seen on server.

I see this perfectly running in Chrome. That tells me I'm not completely off.

I followed it way into the submit / direct submit code. In Internet Explorer 10 debugger I get to class Ext.data.Connection method upload: where it creates an iframe with about:blank and then calls form.submit(). I tried it both leaving my relative url, and then an absolute URL. Same server as web page, same port.

Any known points to watch out for?