Do you see any error messages if you run icedove from an X terminal? You
should also check ~/.xsession-errors.
Did you really complete the upgrade or did apt list some packages as
"kept back"? If you have aptitude installed you can use
aptitude search '~U' | wc -l
Also tell us which version of icedove you are currently using.
(Run "apt-cache policy icedove" to find out.)