Why is package 'xul-ext-ubufox' is required to install the Firefox package?

Summary:

If you want to install a package (here firefox) without automatically having to install its recommendations (here xul-ext-ubufox), you must use apt-get's --no-install-recommends parameter:

sudo apt-get install --no-install-recommends firefox

Detailed explanation:

The package xul-ext-ubufox integrates Firefox better into the Ubuntu OS in several ways. It is a recommended package of firefox, according to the (shortened) output of:

$ apt-cache show firefox
Package: firefox
Priority: optional
Section: web
Installed-Size: 100442
Maintainer: Ubuntu Mozilla Team <[email protected]>
Architecture: i386
Version: 40.0+build4-0ubuntu0.15.04.1
Replaces: kubuntu-firefox-installer
Provides: gnome-www-browser, iceweasel, www-browser

Depends: lsb-release, libasound2 (>= 1.0.16), libatk1.0-0 (>= 1.12.4), libc6 (>= 2.17), libcairo2 (>= 1.2.4), libdbus-1-3 (>= 1.0.2), libdbus-glib-1-2 (>= 0.78), libfontconfig1 (>= 2.9.0), libfreetype6 (>= 2.2.1), libgcc1 (>= 1:4.1.1), libgdk-pixbuf2.0-0 (>= 2.22.0), libglib2.0-0 (>= 2.31.8), libgtk2.0-0 (>= 2.24.0), libpango-1.0-0 (>= 1.22.0), libpangocairo-1.0-0 (>= 1.14.0), libstartup-notification0 (>= 0.8), libstdc++6 (>= 4.9), libx11-6, libxcomposite1 (>= 1:0.3-1), libxdamage1 (>= 1:1.1), libxext6, libxfixes3, libxrender1, libxt6

Recommends: xul-ext-ubufox, libcanberra0, libdbusmenu-glib4, libdbusmenu-gtk4

Suggests: fonts-lyx

Filename: pool/main/f/firefox/firefox_40.0+build4-0ubuntu0.15.04.1_i386.deb
Size: 42549576
[...]

I tried to highlight the important lines for you by separating them with blank lines. A package may ask for other packages in 3 ways: It can depend on, recommend or suggest them.

• Dependencies are required for a package to run and must be installed anyway. There's no way around this.
• Recommendations are packages that should usually also be installed along with the main package, but are not highly required to run. You might omit them if you want, but by default apt-get installs them as if they were true dependencies.
• Suggestions are not installed automatically, they just get displayed and you might consider installing them manually yourself if you want.

As xul-ext-ubufox is a recommended package of firefox, apt-get wants to automatically install it when you try to get Firefox. To stop this behaviour, you must use the following command, which disables the automatic installation of recommended packages for this single time:

sudo apt-get install --no-install-recommends firefox