Uninstalling firefox-esr on Debian 9.3 installs thunderbird and vice-versa

Question

I have an older Intel Atom laptop on which I've recently installed the i386 version of Debian 9.3.1. I'm running it headless, and have no need for Firefox. Much to my surprise, when I did,

sudo apt-get remove firefox-esr

the system removed firefox and installed thunderbird (and also lightning). I then did,

sudo apt-get remove lightning
sudo apt-get remove thunderbird

and the second command above removed thunderbird as expected, and reinstalled firefox-esr.

Is there some way to not have both of these applications? Perhaps there is some dependency elsewhere that can be satisfied by either firefox or thunderbird, thus removing one installs the other?

Solution

You probably have a XUL extension installed; they depend on Firefox or Thunderbird.

apt list --installed xul-ext-\*

will list any installed extensions.

aptitude why will also tell you what’s keeping a package installed.

Comments

[multithr3at3d]

What happens when you remove them all in a single command?

[Stefan Vorkoetter]

That was it, thanks! Tracing through the sequence of "why"s, it seems that I'll lose some desktop functionality (if I ever fire up X) if I uninstall that... Actually, it looks like I'll just lose the ability to run the desktop in Finnish, which is okay, since I don't know Finnish. :-)

[Stephen Kitt]

What functionality would you lose? It should be possible to have a system without Firefox and Thunderbird without losing functionality... (I just checked, removing Firefox and Thunderbird on Debian 9 only removes related extensions, nothing else depends on them.)

[Stefan Vorkoetter]

Well, 'apt list --installed xul-ext-*' returned 'xul-ext-mozvoikko', and 'apt why xul-ext-mozvoikko' returned, live-task-localisation-desktop and task-finnish-desktop. At first I misread the latter as 'finish' (as in done, close, exit), but then just realized it was a language pack of some sort. So I removed xul-ext-mozvoikko.