Assuming you have tried in other browsers to test whether it is Firefox in your case (and assuming you still have the issue?). We have same issue and it fails in all browsers. It appears to be a problem with the routing through a Riverbed Steelhead appliance in our case. I can change my PC default gateway and bypass the riverbed, going directly to our firewall instead. Barclays then works ok. Cant yet see where the problem is coming from though as riverbed is managed by ISP.