If, using gnome-network-preferences, you configure the proxy use use "automatic proxy configuration", then you end up with something like: /system/http_proxy/use_http_proxy = true /system/http_proxy/host = "" /system/proxy/autoconfig_url = file:///home/markmc/.proxy.pac and gnome-session sets http_proxy to "http://:8080" This would fix it: if (host == NULL || host[0] == '\0') { g_unsetenv ("http_proxy"); return; } Look at this, though: http://bugzilla.gnome.org/show_bug.cgi?id=343811 There may be a bit more too it ... there may be a bit more to interpreting the proxy settings
another interesting bit, is there is now code out there that will break down an autoconfiguration url into it's peices using gecko's javascript engine. At some point we may want to think about using that to make http_proxy work in those situations (or maybe not worth the effort) http://mail.gnome.org/archives/gnome-announce-list/2006-October/msg00071.html
I'm going to go ahead a close this. We can figured out the autoconfiguration half later.