zTo find the reverse dependencies you can install the apt-rdepends package:

sudo apt-get install apt-rdepends

You can then search for reverse dependencies using:

$ apt-rdepends --state-follow=Installed --state-show=Installed -r firefox
Reading package lists... Done
Building dependency tree       
Reading state information... Done
firefox
  Reverse Depends: firefox-globalmenu (= 20.0+build1-0ubuntu2)
  Reverse Depends: firefox-gnome-support (20.0+build1-0ubuntu2)
  Reverse Depends: lightdm-remote-session-uccsconfigure (1.1-0ubuntu2)
  Reverse Depends: xul-ext-unity (>= 2.4.7bzr13.04.15-0ubuntu1)
  Reverse Depends: xul-ext-webaccounts (>= 0.4.5-0ubuntu4)
firefox-globalmenu
firefox-gnome-support
lightdm-remote-session-uccsconfigure
xul-ext-unity
xul-ext-webaccounts

To find the reverse dependencies you can install the apt-rdepends package:

sudo apt-get install apt-rdepends

You can then search for reverse dependencies using:

$ apt-rdepends --state-follow=Installed --state-show=Installed -r firefox
Reading package lists... Done
Building dependency tree       
Reading state information... Done
firefox
  Reverse Depends: firefox-globalmenu (= 20.0+build1-0ubuntu2)
  Reverse Depends: firefox-gnome-support (20.0+build1-0ubuntu2)
  Reverse Depends: lightdm-remote-session-uccsconfigure (1.1-0ubuntu2)
  Reverse Depends: xul-ext-unity (>= 2.4.7bzr13.04.15-0ubuntu1)
  Reverse Depends: xul-ext-webaccounts (>= 0.4.5-0ubuntu4)
firefox-globalmenu
firefox-gnome-support
lightdm-remote-session-uccsconfigure
xul-ext-unity
xul-ext-webaccounts

To find the reverse dependencies you can install the apt-rdepends package:

sudo apt-get install apt-rdepends

You can then search for reverse dependencies using:

$ apt-rdepends -r firefox | grep Reverse
Reading package lists... Done
Building dependency tree       
Reading state information... Done
  Reverse Depends: browser-plugin-packagekit (>> 0.7.6-3ubuntu1)
  Reverse Depends: chemical-structures (2.2.dfsg.0-8)
  Reverse Depends: deejayd-webui-extension (0.9.0-4ubuntu2)
  Reverse Depends: firefox-dbg (= 20.0+build1-0ubuntu2)
  Reverse Depends: firefox-dev (= 20.0+build1-0ubuntu2)
  Reverse Depends: firefox-globalmenu (= 20.0+build1-0ubuntu2)
  Reverse Depends: firefox-gnome-support (20.0+build1-0ubuntu2)
  Reverse Depends: firefox-launchpad-plugin (0.5)
  Reverse Depends: firefox-testsuite (= 20.0+build1-0ubuntu2)
  Reverse Depends: gcu-plugin (0.12.12-1ubuntu2)
  Reverse Depends: gnome-core (>= 1:3.4+7ubuntu4)
  Reverse Depends: gosa-desktop (2.7.4-4.2)
  Reverse Depends: lightdm-remote-session-uccsconfigure (1.1-0ubuntu2)
  Reverse Depends: mediatomb (0.12.1-0ubuntu5)
  Reverse Depends: mozplugger (1.14.5-1)
  Reverse Depends: pytrainer (1.9.1-2)
  Reverse Depends: sugar-firefox-activity (6+dfsg-0ubuntu2)
  Reverse Depends: ubuntu-online-tour (0.11-0ubuntu4)
  Reverse Depends: webhttrack (3.46.1-1)
  Reverse Depends: wysihtml-el (0.13-5.1ubuntu2)
  Reverse Depends: xul-ext-mozvoikko (>= 2.0.1-0ubuntu1)
  Reverse Depends: xul-ext-unity (>= 2.4.7bzr13.04.15-0ubuntu1)
  Reverse Depends: xul-ext-webaccounts (>= 0.4.5-0ubuntu4)
  Reverse Depends: libreoffice-subsequentcheckbase (1:4.0.2-0ubuntu1)
  Reverse Depends: libgcu-dbg (= 0.12.12-1ubuntu2)
  Reverse Depends: gnome (= 1:3.4+7ubuntu4)
  Reverse Depends: gnome-desktop-environment (>= 1:3.4+7ubuntu4)
  Reverse Depends: mozvoikko (2.0.1-0ubuntu1)

zTo find the reverse dependencies you can install the apt-rdepends package:

sudo apt-get install apt-rdepends

You can then search for reverse dependencies using:

$ apt-rdepends --state-follow=Installed --state-show=Installed -r firefox
Reading package lists... Done
Building dependency tree       
Reading state information... Done
firefox
  Reverse Depends: firefox-globalmenu (= 20.0+build1-0ubuntu2)
  Reverse Depends: firefox-gnome-support (20.0+build1-0ubuntu2)
  Reverse Depends: lightdm-remote-session-uccsconfigure (1.1-0ubuntu2)
  Reverse Depends: xul-ext-unity (>= 2.4.7bzr13.04.15-0ubuntu1)
  Reverse Depends: xul-ext-webaccounts (>= 0.4.5-0ubuntu4)
firefox-globalmenu
firefox-gnome-support
lightdm-remote-session-uccsconfigure
xul-ext-unity
xul-ext-webaccounts