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. Download an older version of Firefox here.If you know better and don't want to heed their warnings, then do these steps: I did not manually uninstall Firefox, but was prepared for things to go sideways. I rolled back a longstanding, many times upgraded, Firefox 57 to the specific version and bit depth below. In fact, on their support page for the subject, they strongly insist that you do not roll back. There is no built-in rollback or downgrade function within Firefox.

Mozilla firefox esr 52.5.0