Oh dear. I unwittingly updated to Firefox/Iceweasel 29 in Debian testing. What a mistake! My Firefox setup has remained basically the same since the 3.5 days with a nice unobtrusive layout where I have the menu, navigation buttons, and the address bar in one strip and the tabs below. Despite hours of hair pulling there’s no way to get anything remotely satisfactory with the new UI, even with the “Classic Theme Restorer” addon.
Panic not! It’s possible to just stick with the stable 24.4 version from Debian wheezy! For future reference, this needs to go into
deb [arch=amd64] http://security.debian.org/ wheezy/updates main
Then do this:
sudo apt-get install -t wheezy iceweasel sudo apt-mark hold iceweasel
UPDATE: I later upgraded to 31 ESR and worked around most of the problems.