Firefox keeps prompting for Proxy Authentication

I have been facing this for a long time since 3.5. something.  Even after upgrading to 3.6 it continues.  Firefox would keep on asking for proxy authentication even though i had given the id and password and even it remembers.  But it will always ask for the id and password.  Today looked around to find a solution, and i came across this, which seems to working.  No popups for authentication for the past 2 or 3 hours.  go to about:config and search and the following properties.

network.proxy.share_proxy_settings – FALSE
network.automatic-ntlm-auth.allow-proxies – FALSE

You can read the full discussion here

update:

Setting these properties alone does not work.  you have to set one more property.

network.auth.use-sspi – FALSE

These setting works in Flock & Thunderbird 3 also.