Really, I think Firefox deserves mostly cheers. I reserve most of my jeers for lousy extensions or extension incompatibilities. (That, despite the fact that I know how hard it is to write code that will Just Work when plugged into an existing larger system with other plugins.)
After reading more about Tab Mix
which Shawn also suggested, I decided to give it a try. It said it wasn't
compatible with Session Saver
Maybe I could have taken less drastic measures, but I didn't feel like researching it. Fortunately, I had the foresight to back up my session before this whole mess, so once I was back up and had my extensions set up, a little bit of Vim magic got my tabs and windows back in place.
I didn't just use the same set of extensions on this new profile. I skipped Tab X (for a "close" button on each tab) and Session Saver, and went right to Tab Mix Plus. I think this was a good choice. TMP seems a little slow, but it works well. One thing it doesn't do, much to my chagrin, is allow me to drag a tab from one window to another to move it. Instead, dragging a tab will copy it, so that I must then go and close it in the original window. I can live without OmniWeb's "select, cut, paste" operations on tabs, but I really wish basic drag and drop was more reasonable.