Question about proxy authentication in Firefox1.0

Hi,

I am working with Mozilla firefox 1.0 within a windows XP environment.
I have configured the proxy settings successfully and can browse the
internet.

Whenever I browse to certain site where I have to authorize myself, a
second dialog pops up. This dialog asks me to provide username and pw
for the proxy through which I connect. I have checked the checkbox,
which allows the paswordmanager to take care. But it still keeps
popping up where username and password filled have been filled in.
What I want is that this dialog shuts up and just provides this logon
information to the proxy without bothering me. SOmeone knows how to do
this?

greetings en thnx,