Hallo David. Thanks for your reply. I have the latest version that you mention. The add on that Mozilla is blocking is Avast Online Security 12.0.163. It has been disabled ‘not certified for use’. I don’t know what this add on does or if it matters that it is blocked. Am I still protected? I have noticed that about a dozen Avast api-ms-win-core-console I1-1-Odl app ext have been downloaded by Avast. Do I need all these? Many thanks. Indigogreen