sudo dpkg -i --force-overwrite  /var/cache/apt/archives/firefox_20.0+build1-0ubuntu0.12.10.3_i386.deb
(Reading database ... 99308 files and directories currently installed.)
Unpacking firefox (from .../firefox_20.0+build1-0ubuntu0.12.10.3_i386.deb) ...
dpkg: warning: overriding problem because --force enabled:
 trying to overwrite '/usr/share/applications/firefox.desktop', which is also in package kubuntu-firefox-installer 12.04ubuntu1
dpkg: dependency problems prevent configuration of firefox:
 firefox depends on libstartup-notification0 (>= 0.8); however:
  Package libstartup-notification0:i386 is not configured yet.

dpkg: error processing firefox (--install):
 dependency problems - leaving unconfigured
Processing triggers for man-db ...
Errors were encountered while processing:
 firefox