Is there a deb package to install Firefox ESR?

It has a PPA here, but it is not launched yet, so we have to install it manually:

I suppose that you have a 32bit edition on Ubuntu, and you are using English language:

• Let's download it:

  wget ftp://ftp.mozilla.org/pub/mozilla.org/firefox/releases/10.0.2esr/linux-i686/en-US/firefox-10.0.2esr.tar.bz2
  

• We will extract it to /opt:

  sudo tar -xvjf firefox-10.0.2.tar.bz2 -C /opt
  

• Let's move away the normal Firefox link:

  sudo mv /usr/bin/firefox /usr/bin/firefox-old
  

• Linking the new Firefox:

  sudo ln -s /opt/firefox/firefox /usr/bin/firefox
  

That's it. Enjoy!

Note: if you want to upgrade afterwards, launch it with gksudo firefox, and choose Help > About Firefox menu, and see if any updates are available. If yes, apply them.

For Ubuntu Trusty and Xenial exists new Jonathon F's PPA.

sudo add-apt-repository ppa:jonathonf/firefox-esr
sudo apt-get update
sudo apt-get install firefox-esr

It maybe very useful because of new Firefox add-on policy.
I have installed 10 add-ons and 9 of them are marked as LEGACY.

There is a semi-official ppa now, I suggest to use this. There is also a description how to add and get it automatically update.

https://launchpad.net/~mozillateam/+archive/ubuntu/ppa