Modal dialog closing

Hi i'm trying out the Dialog Modal form example as seen on
http://jqueryui.com/demos/dialog/#modal-form
but every time i click the 'Create new user button' the modal form
comes up up ok, but then it just closes. I downloaded the lasted
version of jquery plus the UIs with all the events and all. Oh, by the
way this only happens in Firefox. It works great in IE7.
Can anyone tell me wat is going on?