[8.960] Upload files via browsers

Hi,

I'm on firmware 8.960-9.

I use Web Protection using the port 3128 for several services : http, https, ftp...
I've got a special Nic and IP for the proxy.

When i try to upload files on upload services like imageshack.us or several blog systems, i've got an authentification request by the proxy.

I've got the problem using Firefox, Chrome but not with Internet Explorer.

I see nothing on logs....:confused:

Thank you for your help.