Later OK. It's now sorted, and I know what happened.
In Facebook, I got a message about a video I had been sent, and when I accessed it, it told me to update Flash. My system was iffy about the publisher of what was alleged to be Flash and I did not download it - but it obviously got into my system anyway...Because when I looked for various things that were coming up in the redirections, like 'findmycontent', they turned out to relate to a hijacker which goes by the name of tinyproxy1.exe, which has nothing to do with the totally reputable programme tinyproxy. I removed it, but then was unable to get into Firefox.
With help from the wonderful Erin, I found the proxy setting in Firefox it had altered, and the dodgy bits of itself it had installed in startup and registry.
Right now I want to kill the people who devise these instruments of torture, and all the commercial sites that use them to pull in punters. I have wasted most of a day, and sat up late last night, trying to get this sorted out.