The browser itself is something we wrote, the mechanism that “installs” the projects is actually the underlying Eclipse CVS support — when you click the “Install” button, it fires off a CVS checkout on that project from our repository — if you witch to the CVS view you can see our repository listed there… so if there is a bug in there, unfortunately that would fall on the Eclipse CVS team’s shoulders to fix.
The CVS connection stuff should honor your proxy settings under Window > Prefs > General > Network Connections.