Comment 3 for bug 1676164

This problem is very actual.
It was discussed at least twice on AskUbuntu (see https://askubuntu.com/questions/305199/is-there-a-deb-package-to-install-firefox-esr and https://askubuntu.com/questions/505895/how-can-i-install-an-older-version-of-firefox-in-ubuntu-14-04 ).

For Ubuntu Trusty and Xenial exists new Jonathon F's PPA (https://launchpad.net/~jonathonf/+archive/ubuntu/firefox-esr).
Users can install Firefox ESR with the following commands:

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

Thank you, jonathonf!

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 (see https://support.mozilla.org/en-US/kb/firefox-add-technology-modernizing ).

So for enterprise users we really need ESR version of Firefox.
Please make official Ubuntu package with it.