My home-baked CyanogenMod 10 ROM is working fine.  Titanium Backup replaced all my old files with no problems and this time Firefox is working normally.  I must have installed the wrong google apps package last time.  Here is the right google apps.

Minor issues:

1. When I was typing I had two keyboards showing to select the input method.  I think one was android and one swiftkey.  I disabled the android one in settings (Settings > Language & Input > Selector notification: OFF)
   
2. I still cannot get Ubuntu to see all the files on the tablet.  Plug in to Windows and I see everything, but in Ubuntu I have done the required fiddling but still can only see a small subset of the folders.
3. superuser was continually force closing.  It was good enough to give me access to root privileges, but could not remember them.  I found this page with an updated superuser, and it seems to work.  I tried to find superuser.apk in the backup, but it wasn’t obvious.  One for another day.