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I might have sorted it now, after a long wander round. After being unable to activate firefox, I looked in Google and tried Stopzilla, which looked good, but after downloading it, they wanted $19.99. So I went back to Firefox. I uninstalled Stopzilla, and tried again to activate Firefox and, at the present time I'm not certain whether it is 'on'. Anyway, during all this I clicked on 'tools', and there in the drop-down is "pop-up blocker.".....so obvious! So I have clicked 'turn on blocker', and so far things seem to be OK. So thanks for your help. Ian