I couldn’t read any web pages because I shut down firefox hours ago
(thinking I was upgrading it) and then it (the older version) wouldn’t start again. But then I just solved the yum problem, upgraded several apps (including firefox) and the new firefox is working now.
All I did was put the original /var/lib/rpm/Packages file back where it was. (If you read from a post from earlier today, I mv’d off this file and then ran rpm –rebuild to recreate it. This fixed the problem with yum hanging, but then I was getting crazy error messages from yum and from rpm.) Something told me to put the original Packages file back where it was, I did, and now yum works again. And the just-upgraded firefox works too.
Thanks to you and everyone else who responded. I have to say, I still don’t know what caused the problem in the first place. But sometimes things just have to be a mystery.