Firefox was definitely clobbered. It wouldn't open more than one window at a time. It has a weird icon. Tab Mix Plus was a non-starter.
I uninstalled all add-ons, then reinstalled them in the order that I needed them. It seems to be working again except for the icon. If I mouse over the icon, it displays as firefox, so I guess I can live with it.
On to figure out how to reconfigure the title bar controls...