If you go to about:policies in the address bar, do you see any active Enterprise Policies?

Have you tried uninstalling and reinstalling Firefox?

If you go to about:policies in the address bar, do you see any active Enterprise Policies? Have you tried uninstalling and reinstalling Firefox?

"The Enterprise Policies service is inactive." Nothing there. Already tried different installations and profiles, too.

What is the screenshot of the settings where your making these changes at? That might help others look to see what it's doing. And sometimes updates defaults settings back to standard to do proper updates - that's something to consider as well.

It's the only out of I don't know how many settings that gets changed and that has happened with every single of the hundreds of updates I've done over the years.

Preferences would normally only get reset if there is a problem with accessing prefs.js in the profile folder. Do you have multiple numbered prefs-##.js files in the Firefox profile folder that could indicate a problem ?

You can check for problems with preferences. You can delete possible user.js and numbered prefs-##.js files and rename/remove the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in current Firefox releases.

You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page (Root directory).

• Help -> More Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

See also:

• https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

If you can't figure out what is tampering with the telemetry setting (datareporting.healthreport.uploadEnabled) on your system, you can lock it with Enterprise Policies. Create a "policies.json" file and place it in a folder called "distribution" in the installation folder where firefox.exe is located containing:

 {
   "policies": {
     "DisableTelemetry": true
   }
 }

Preferences would normally only get reset if there is a problem with accessing prefs.js in the profile folder. Do you have multiple numbered prefs-##.js files in the Firefox profile folder that could indicate a problem ? You can check for problems with preferences. You can delete possible user.js and numbered prefs-##.js files and rename/remove the prefs.js file to reset all prefs to the default value including prefs set via user.js and prefs that are no longer supported in current Firefox releases. You can use the button on the "Help -> More Troubleshooting Information" (about:support) page to go to the current Firefox profile folder or use the about:profiles page (Root directory).

• Help -> More Troubleshooting Information -> Profile Folder/Directory:
  Windows: Open Folder; Linux: Open Directory; Mac: Show in Finder
• https://support.mozilla.org/en-US/kb/profiles-where-firefox-stores-user-data

See also:

• https://support.mozilla.org/en-US/kb/how-to-fix-preferences-wont-save

Only one file there.

If you can't figure out what is tampering with the telemetry setting (datareporting.healthreport.uploadEnabled) on your system, you can lock it with Enterprise Policies. Create a "policies.json" file and place it in a folder called "distribution" in the installation folder where firefox.exe is located containing: { "policies": { "DisableTelemetry": true } }

I've just created the file. Will see what happens with the next update.