The debian Name for the Firefox Webbrpwser is Iceweasel. Install it with:
#> apt-get install iceweasel
It seems as Iceweasel and Icedove are not updated and stay at old Versions.
To work around that visit the Page of Debians Mozilla Team at:
http://mozilla.debian.net/
For newer Debian Releases the Repository in the Link above, should be put in a extra File in /etc/apt/sources.list.d/.
To access the Calender also install the iceowl-extension.
Don't forget to disable the Repository afterwards, by adding a # in the Front.
Iceweasel comes with an old Flash Plugin. You can install the newer nonfree Plugin with:
#> apt-get install flashplugin-nonfree