For the past week or so I am finding Youtube videos are unavailable because, I understand from messages that flash on my screen, its ads are being blocked. This does not occur if I use Chrome. Also, although I had chosen Duck Duck Go as my search engine, Yahoo seems to be doing the job. Can you please advise me how I can stop ad blocking for Youtube, and yahoo appearing as the search engine, when I use Firefox. Firefox was my default browser but have changed to Chrome for the present. The O/S on my PC is Windows 10.