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

Thanks for your note. I created a file called "policies.json" with this content: {

 "policies": {
   "DisableAppUpdate": true
 }

}

and put it into the folder where firefox.exe lives: C:\Program Files\Mozilla Firefox

but when I ran FF, it tried to update itself...

Read all of the instructions. Including where to place the file.

Thanks for your reply. I missed this: "On Windows, create a directory called distribution where the EXE is located and place the file there." but just did that, and FF still tries to update itself.

Did you place the policies.json file in the distribution directory of the Firefox program?

Yes I did. I actually had to go back to v65 from 67, and this time it worked! Thanks for the input.

What software does not work with modern versions? Old versions of Firefox have known security holes and should not be used.

I am glad to hear that your problem has been resolved. If you haven't already, please select the answer that solves the problem. This will help other users with similar problems find the solution.

Thank you for contacting Mozilla Support.