For some HTTPS websites, the response will be very slow.
Try install this patch: Update for Windows Vista (KB933228)
If it doesn’t help, try the following:
First: Try to disable “Use TLS 1.0″ in Internet Options.
Second: Try to enable “Use SSL 2.0″ in Internet Options.
Last: If it’s still very slow, try to disable TCP auto tunning by executing the following command in cmd.exe as administrator.
netsh interface tcp set global autotuninglevel=disabled