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Thanks again to everyone who tried to help me although, I must confess, a lot of it went right over my head! My husband tried to find 'extensions' without success and I was about to post again asking for further pointers on where to find it. I mentioned to my husband that there was a java update available - I never know whether to do updates, whether they are safe or not, so he did it. Then he happened to get Downton up on itvplayer and hey presto! the message about ad blocks had gone. I don't understand the reason for it but am just grateful that the message has gone.