http://gurustop.net/blog/2010/08/10/visual-studio-2010-extension-manager-online-gallery-behind-internet-proxy/
I opened this file in Visual Studio (yes, it’s OK – the effected showed after restarting VS of course):
The section I was looking for is under “<system.net>”. The config file already had this section to enable IPv6 (which is not enabled by default, yet another interesting default and override – I commented the override anyway later).
<system.net>
>
<proxy usesystemdefault="True" /></defaultProxy>