In Mozilla FireFox, every time you send a request to the server that has a multipartform-data (using FileReference when uploading a file) the SESSIONID value is not send in the HTTP header. That means that if the application/page/site you are working on is authenticated its not going to work. This only happens in FireFox, IE 6, 7, 8 work fine.
I know must of you are already aware of this FireFox bug. Have anyone found a work-around that doesn't relay on a back-end fix?