There are several posts around the Internet about Firefox returning an I/O error when attempting to use Flash upload applications on a web site that has a self-signed SSL certificate. There are no reported solutions from Mozilla.

Performing the exact same Flash upload operation on Internet Explorer completes successfully for a https:// site that has a self-signed certificate.

I only use IE Explorer when absolutely necessary. I'm hopeful Mozilla will choose to fix this annoying issue.

support.mozilla.com/tiki-view_forum_thread.php

bugs.adobe.com/jira/browse/FP-226

swfupload.org/forum/generaldiscussion/92