
At November I wrote a fresh message to this mail list with a link to the current question. The feature request for the official ESR package is located in Launchpad bug 1676164 and on the ubuntu-desktop maillist.You can install the package on 14.04 LTS (Trusty Tahr), 16.04 LTS (Xenial Xerus), 17.04 (Zesty Zapus), 17.10 (Artful Aardvark), and 18.04 LTS (Bionic Beaver) from this repository with the following commands: sudo add-apt-repository ppa:mozillateam/ppa Get Firefox ESR 52.5.0 from Mozilla Team's PPA (the first versions were published here at as the result of discussion on the ubuntu-desktop maillist). You can install the package on 14.04 LTS (Trusty Tahr) and 16.04 LTS (Xenial Xerus) from this repository with the following commands: sudo add-apt-repository ppa:jonathonf/firefox-esr Get Firefox ESR 52.5.0 from Jonathon F's PPA. I think it is better to downgrade to Firefox ESR 52 (this branch is planned to be supported until and will get security updates).

This answer is based on my answer on AskUbuntu - it suggests and describes howto install Firefox ESR 52.5 on Ubuntu and Mint. Restore your backed up profile ( Mozilla Support).Install from the 56.0.2 executable you downloaded.Manually remove the leftovers and profile folder if you have to.Completely uninstall Firefox via Programs and Features.If your install is broken, try the usual steps to fix installation problems: My previous session, extensions, and settings were all as they were before the upgrade/downgrade.Go through the installer, and when its complete, launch Firefox.Find the executable you downloaded in step 1.You can simply copy the folder somewhere else, just in case stuff goes sideways. Also, this Mozilla Support article covers steps 3, 4, and 5 of this answer. You can look at all of their 56.0.2 releases here.

If you are trying to back down from 57, you'll want to grab 56.0.2, (Windows US English version 32 bit exe) here.
