Warning--Icedove 126.96.36.199-3 package broken (+fix)
I just had to go through this, and I don't see any mention of it here, so I'm posting this heads-up. There seem to be some problems when upgrading the Debian unstable package of icedove 188.8.131.52-3. When I did it, my profile data failed to show up and half the controls were broken.
But some comments on the Debian Users mailing lists point to a solution. Simply uninstall the icedove package with the --purge option and reinstall it. Everything should work fine after that. It shouldn't touch your user profiles, so your data should be safe (but it never hurts to have a backup!).