Note: With some versions of Firefox, the data files are not backward compatible. If there is an issue, create a new profile and we can tell you how to recover the data.

Step one: How do you completely turn off update checks in Firefox v64? You can use a policies.json file to disable updates for all users. https://github.com/mozilla/policy-templates/blob/master/README.md or https://winaero.com/blog/disable-updates-firefox-63-above/

You can use a policies.json file in the distribution folder in the Firefox installation folder instead as also listed in the article, so no need to use GPO keys in the Windows Registry. • https://support.mozilla.org/en-US/kb/customizing-firefox-using-policiesjson ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ You can use the ManualAppUpdateOnly policy in Firefox 87+ to enable only manual updates e.g. via "Help -> About Firefox".

• https://github.com/mozilla/policy-templates#manualappupdateonly
• https://support.mozilla.org/en-US/kb/customizing-firefox-using-policiesjson

Note that it is important to stay up to date and install the latest security patches.

• https://www.mozilla.org/security/known-vulnerabilities/firefox.html

Step two: Note: With some versions of Firefox, the data files are not backward compatible. If there is an issue, create a new profile and we can tell you how to recover the data.

Install Older Version Of Firefox {web link} Be sure to read everything here.

If you still want to downgrade, look under; I still want to downgrade. Click the Directory of other versions and languages link. Look for the directory of the version that you want. But, remember that old versions may have security issues.

Note: If you know what version you want, press <Control> (Mac=<Command>) F to open the search bar. Then enter the version number to see the available files.

You should also check out Firefox; Extended Support Release {web link} ESR Notes System Requirements

I really appreciate your concerns. I am not trying to go backwards. I have a 2007 iMac which still serves limited purposes, but current browsers will not run on it, so I am blocked from the internet. I want a version of Firefox that is compatible with the old Core Duo chip and Mac OS 10.5.8.

So it must be version 16 -> https://www.mozilla.org/en-US/firefox/16.0/system-requirements/

Just to be sure: is this a Mac with an Intel processor or a PPC Mac ?

• https://support.mozilla.org/en-US/kb/firefox-no-longer-works-mac-os-x-10-5
• https://download.cdn.mozilla.net/pub/mozilla.org/firefox/releases/16.0.2/mac/

If this is a PPC Mac, see the TenFourFox website (support has halted).

• https://www.floodgap.com/software/tenfourfox/
• https://sourceforge.net/projects/tenfourfox/files/
• https://github.com/classilla/tenfourfox/wiki/ZZFPRReleaseNotes32

The computer told me that the software could not be installed. It has an old Intel Core2Duo chip running on OS 10.5.8.

You are pretty much stuck with the rather old Firefox 16.0.2 from October 26, 2012 as 17.0 required macOS 10.6 at minimum.

Not sure how new a macOS you can install to as it could be macOS 10.6 to upwards of 10.11.x.

One option to have a much more current OS is to install Linux since you have a Intel CPU.

For an example this person may have a similar system to yours https://www.linux.org/threads/installing-linux-on-an-imac.26009/

The computer operating system has no where to go. They retired the CoreDuo chip and it will not upgrade. I just want to use this dinosaur for a few simple tasks and have internet access.

I have a 2007 iMac and need a version of Firefox that will operate on MAC OS10.5.8 To be clear: I am NOT trying to update the computer. It is end-of-life. I just want to use it as a spare and have internet access.

Somehow, this got marked as solved, but it is not.

Well you are stuck with using old vulnerable web browsers from 9-10 years ago. With Firefox 16.0.2 you may have issues with how many sites load and more so with current https:// sites.

You can try Fx 16.0.2 https://archive.mozilla.org/pub/firefox/releases/16.0.2/mac/

If it can run at least macOS 10.9 to macOS 10.11 then you could run Firefox 78.15.0esr as the most current. https://support.mozilla.org/en-US/kb/firefox-mac-osx-users-esr

Otherwise as I mentioned there is the possibility of installing a Linux distro so you can use current software including current Firefox versions like Fx 96.0 and Fx 91.0 ESR.