about Proxy connections and http/https.

In this thread;
the user wasn't able to load http pages in IE7 but, unlike you, was able to see them load in Firefox.

She checked her IE Tools > Internet Options > Connections tab for any proxy connections and found her connections had been changed to proxy. She changed them back and IE started working properly again.

Apparently, as stated by Kees, another Moderator here, "https isn't cached by a proxy (to make it still safer), http is.". Now, I am not exactly sure what that means, but it seems to allow https pages to load, but not http.

Any chance this is the same problem with your browsers?