Norton 360 just offered to install a new version, free. OK, I said. I rebooted when requested.
First, Firefox wouldn't start. I rebooted again.
Firefox opened OK, with the dozens of tabs I'd had open. But I noticed that Firefox didn't seem to remember what sites I'd been on. And there was a new toolbar, which I disabled because it took up a lot of window space.
Next time I rebooted and restarted Firefox, all my tabs were gone. I don't know what I was working on, and I don't know where I've surfed.
I found that "Clear history when browser closes" was checked in my Firefox preferences, including "Clear browsing history." It's obvious that Norton did it. In Norton, I found that "Firefox Cleanup" was on.
Norton has deleted my data without warning me, and messed with the configuration of another program without asking me. That is completely unacceptable.