I have been complaining about being unable to use some apps from behind my corporate firewall, while I was able to use FFox without problems.
Today I discovered why: when you define e.g. proxies set up in FFox it does not update the corresponding setting in the OS, but it merely overlays these settings to the one it receives from the OS. Which means other apps that rely on the OS setting (e.g. Twitter clients) read the wrong settings and are unable to connect.
I’m sure there’s a very good reason for this decoupling, which neither Safari nor, e.g. Cruz adopt, and I need to investigate whether it can be defaulted to the OS settings.