FF portable not working with "Blue Coat"

Our company recently added "Blue Coat" security to its network. For those who don't know, it's kind of like "Net Nanny" for employees: It prevents access to many websites the employer thinks you should not be visiting at work.

Anyway, after they did this, my FF portable no longer works! After launching FF as usual from my usb drive, a Windows XP authentication window pops up and requests "Enter User Name" for an unknown url at our facility, and a "Password". This window cannot be closed. I must terminate the FF process.

Any help with this would be appreciated!