1. Please install the silverlight or flash plug-in for your firefox browser.
2. You can see all the file type in the select file dialog, but once you choose the file for upload, the uploader control will shows you the message, file type do not allow. And will disable the upload.
We achieve the filter function on server side and client side both. The client side filter like what you see in the select file dialog is based on silverlight and flash plug-in. If your browser has not install the silverlight or flash plug-in, then it will switch the IFrame mode directly. The IFrame mode does not support to filter the file at client side, so we will filter the upload file at server side.