Upload Progress Event Trigger Exception

This occurs because Firefox provides an input property on the progress event, but doesn't actually implement it and instead throws an error if it's accessed.

_trigger() is only meant to receive jQuery events, not native events. You should bind to the progress event with $( xhr.upload ).bind( "progress", ... ) and pass the jQuery event to _trigger(). If you want the progress-specific event properties to be copied to the new event, you'll need to define $.event.fixHooks.progress. The minimal implementation for your test case would be:

$.event.fixHooks.progress = {
    props: ["loaded"]
};

Thanks, understood.

I think the _trigger documentation on the Wiki page is a bit misleading, if only jQuery events are expected:

"You may also provide an event object that represents the event that initiated the process. For example, a drag event is initiated by a mousemove event, so the original mousemove event object must be passed in to _trigger."

http://wiki.jqueryui.com/w/page/12138135/Widget-factory

Yes, that's definitely misleading and the newer WIP docs were actually wrong. I've updated the WIP: https://github.com/scottgonzalez/widget-factory-docs/commit/9cae83cbb08d5fcc72ab11022262141e7107fb91

Thanks. :)