Iceweasel reinstall - defect package

[complAxx]

Hey Guys =)
so i installed Kali yesterday, and i didnt like the Iceweasel browser, so i installed firefox and chromium and uninstalled iceweasel.
then i decided i don't like gnome-fallback either, and wanted to install gnome 3. I found a nice guide too, and did this:

root@kali:/home/oxymoronist# apt-get install gnome-core kali-defaults kali-root-login desktop-base
Reading package lists... Done
Building dependency tree       
Reading state information... Done
desktop-base is already the newest version.
desktop-base set to manually installed.
gnome-core is already the newest version.
kali-defaults is already the newest version.
kali-root-login is already the newest version.
You might want to run 'apt-get -f install' to correct these:
The following packages have unmet dependencies:
 gnome-core : Depends: iceweasel (>= 10) but it is not going to be installed
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).
root@kali:/home/oxymoronist# apt-get -f install iceweasel
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  libmozjs22d openjdk-7-jre-lib python-apsw xulrunner-22.0
Use 'apt-get autoremove' to remove them.
Suggested packages:
  fonts-oflb-asana-math fonts-mathjax mozplugger
The following NEW packages will be installed:
  iceweasel
0 upgraded, 1 newly installed, 0 to remove and 10 not upgraded.
2 not fully installed or removed.
Need to get 0 B/2,870 kB of archives.
After this operation, 7,034 kB of additional disk space will be used.
(Reading database ... 371903 files and directories currently installed.)
Unpacking iceweasel (from .../iceweasel_24.5.0esr-1~deb7u1_i386.deb) ...
dpkg-divert: error: `diversion of /usr/bin/firefox to /usr/bin/firefox.real by iceweasel' clashes with `diversion of /usr/bin/firefox to /usr/bin/firefox.ubuntu by firefox-mozilla-build'
dpkg: error processing /var/cache/apt/archives/iceweasel_24.5.0esr-1~deb7u1_i386.deb (--unpack):
 subprocess new pre-installation script returned error exit status 2
Processing triggers for menu ...
Errors were encountered while processing:
 /var/cache/apt/archives/iceweasel_24.5.0esr-1~deb7u1_i386.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)
root@kali:/home/oxymoronist# apt-get -f install gnome-core kali-defaults kali-root-login desktop-base
Reading package lists... Done
Building dependency tree       
Reading state information... Done
desktop-base is already the newest version.
desktop-base set to manually installed.
gnome-core is already the newest version.
kali-defaults is already the newest version.
kali-root-login is already the newest version.
You might want to run 'apt-get -f install' to correct these:
The following packages have unmet dependencies:
 gnome-core : Depends: iceweasel (>= 10) but it is not going to be installed
E: Unmet dependencies. Try 'apt-get -f install' with no packages (or specify a solution).
root@kali:/home/oxymoronist#

what else can i try? gnome 3 seems to be installed, but does not work - instead gnome-fallback is running. there comes an error message that gnome3 does not work and instead gnome-fallback is running (i LOVE sentences like these).
gnome is dependent on Iceweasel, i guess, but iceweasel is defect. so installing Iceweasel should fix the problem, right? but how? apt-get -f install does not work.

thank you, complAxx