Tried again today. Instant drop out with the no activity in the last 10 minutes message (total lie!) when I click the *allow new page* button.
As a check, I installed Safari (there is no need to faint) and it worked fine. Stayed logged in and printed off lots of PDF statements so I was in there more than 10 minutes.
Something amiss with my version of Firefox. Cookies are allowed and nothing obvious in the security settings. Mind you, the weekly multimeg upgrade is getting tedious.
I need to drop this now but can manage with Safari. Thanks to all who responded.