As you may know, Iceweasel is the equivelent of Firefox and Icedove is the same as Thunderbird, on Debian Systems.
Firefox and Thunderbirds are open-source projects, so there is no problem with using it, but because of some licence issues in the past, from Debian Lenny (I think), the Mozilla programs got the 2 different names and logos.
You have to do a few tweaks if you want to keep up to date Iceweasel and Icedove on Debian Systems.
Step 1: Add this line to /etc/apt/sources.list.d /iceweasel.list:
$ sudo echo ‘deb http://cdn.debian.net/debian experimental main’ > /etc/apt/sources.list.d/iceweasel.list
Step 2: Download and install the authentification key:
$ wget -c http://mozilla.debian.net/pkg-mozilla-archive-keyring_1.1_all.deb
$ sudo dpkg -i pkg-mozilla-archive-keyring_1.1_all.deb && rm pkg-mozilla-archive-keyring_1.1_all.deb
Step 3: Update the repo index:
$ sudo apt-get update
Step 4: Install the latest versions of Iceweasel and Icedove:
$ sudo apt-get install -t experimental iceweasel
$ sudo apt-get install -t unstable icedove
This is it. Now you can update Iceweasel and Icedove successfully.