Hey there!

Please see the following link below on how you can install the previous version of Firefox:

https://support.mozilla.org/en-US/kb/install-older-version-firefox

Hope I helped!

Kind regards,

Bithiah

I have done all this stuff.

What is the trigger that gives me the error message when I try to run the newly installed older version? I keep going back in time installing older versions of Firefox and when I try to run the older version, I still get the same error message.

Something must be sitting on my machine that does not get removed by doing an uninstall. I went back to a version for 10.0.9, and I still get the same error message. It does not seem to matter what old version I install.

See the image below at run time. - Thanks Rod

Do you still have the install file? Make sure you removed the updated version that doesn't work for you.

I have about 6 copies of the .dmg files for various releases in my download directory. Are you saying that getting rid of them will help?

I have un-installed versions and installed a older release. The same message comes up. So my theory is that there is a text file left somewhere or some other trigger file that the un-install does not get rid of.

If I could upgrade the OS, I would. but this is a 2008 Mac running Catalina. So I would have to buy a new machine to get rid of this problem??

You can keep the old files if you want, but I advise you to store them not in the Applications folder.

So I went back and installed Version 78. That did not work either. So I tried Firefox 10.0.11esr.dmg, 10.0.9esr.dmg, and even Firefox.45.9.0esr.dmg. After install, I get the same message. You can't use this version of the application Firefox with this version of OS. You have 10.11.6, This application requires 10.12 or later.

https://www.mozilla.org/firefox/78.0/system-requirements/ Operating Systems macOS 10.9 macOS 10.10 macOS 10.11 macOS 10.12 macOS 10.13 macOS 10.14 macOS 10.15

Firefo 78.0.15 esr should run on Mac OS X 10.11 as Fx 79.0 and later requires macOS 10.12 or later. https://archive.mozilla.org/pub/firefox/releases/78.15.0esr/mac/en-US/ for other language locales https://archive.mozilla.org/pub/firefox/releases/78.15.0esr/mac/

Fx 78.0.15esr released on October 5, 2021 is the last update for the old Fx 78.0 ESR channel.

Also make sure only the one version is installed as perhaps you have two or more and is starting the wrong version.

I have been doing un-installs by dragging the app to the trash bin. So I think I only have one version installed.

I'm at a loss as what else to try. It doesn't seem to matter how far back in FIrefox versions I go. The runtime problem is the same. Here is the 'about my MAC' in the accompanying jpeg.