Firefox is configured to use a script to determine the proxy configuration. I can't really describe the config script, it's provided by the company and I can't post it here as I'm sure it could be considered proprietary information as it contains domain names and IP addresses. Basically, the script is hosted on the company network, when it can be found (either on-site or when through the VPN) it configures the proxy, if it can't be found it goes "proxy-less". Again, as long as the proxy is configured for one requiring authentication, I get a secondary proxy authentication that has moz-proxy appended to the beginning of the proxy server, attempts to authenticate result in the same box looping with authentication never occurring. When I cancel the auth request FF crashes. FWIW, FF started crashing in the last couple weeks, I finally got to the point of building a new profile for FF and then reinstalling Windows to resolve the issue. The crashes and this proxy issue seem to coincide with the update to 7. I used MozBackup to backup and restore ONLY my bookmarks, saved passwords and certificates.