Thanks - there was one malware on board 'adware.shopper', I got rid of it. Fairly innocuous but it might have been responsible for the odd browser window behaviour? The malware is almost certainly a direct consequence of Adobe Flash 11 which is basically dysfunctional. In desperation I (and many others) have been looking for ways to download videos which won't play properly on Flash any more. Green light to malware - thanks Adobe :-|
Will update if necessary.