you cant open subdirs with firefox 8.0 on your demo page (file dialog)
and the files are to small (file size) to get the error.
try and make a dir with larger .pdf or .doc files (not images) lets say about 100mb and you will get the same error .
the dialog box will take forever to come up or crash.
on windows 2008 iis 7.5
browser tested: chrome, ie9, firefox 8
on which version is you demo application running ? (windows, iis)
on my local windows 7 iis 7 system the file dialog works
but on my windows 2008 iis 7.5 system the file dialog didnt work