Older Versions of Firefox

[StephenLeggatt]

Mozilla talks as if an upgrade to the new version is vital and you are  kind of dumb and at risk if you ignore this warning, whereas if you have an older Mac running El Capitan, short of spending $5,000 on a new Mac, you have no choice but to stay on the old version since new Firefox will not run. Also there is no test or warning that the upgrade will not work on your machine or that it will delete your old version. This just happens and tough luck.

There are articles on getting back the older version but no easy one stop shop e.g. where it says "downloads here"

[jscher2000]

If your version of Firefox isn't compatible with the update, I'm surprised Firefox would auto-update. ???

The .dmg file for your version of MacOS can be found here:

https://archive.mozilla.org/pub/firefox/releases/78.15.0esr/mac/en-US/

If you are looking for a different language-locale (other than English US), click the little .. link on that page to move up to the folder listing all the available locales and then click into the one you want.

Once you have the .dmg file, it's the usual steps for the installation: https://support.mozilla.org/kb/how-download-and-install-firefox-mac