Hello, these customized about:config prefs you've said should not change when Firefox updates. Only if the pref is removed should it change.

Changes made from the default in about:config or in Options/Preferences or Addons manager are written to the prefs.js file in your Profile.

http://kb.mozillazine.org/prefs.js_file

This is why doing a Refresh will clear these settings as it is basically a awkward way of making a new Profile instead of just using the ProfileManager to do so.

James said

Changes made from the default in about:config or in Options/Preferences or Addons manager are written to the prefs.js file in your Profile. http://kb.mozillazine.org/prefs.js_file This is why doing a Refresh will clear these settings as it is basically a awkward way of making a new Profile instead of just using the ProfileManager to do so.

Hello James, thank you for responding. This response does not answer my question, but the fault is mine, as I included too much extra information in my question. My apologies. I should have only written this: "My question is, will the changes we make in about:config be lost when Firefox updates?"

(additional thanks to Mkll, but the phrase 'will not change' would be much more reassuring than 'should not change').

That is not going to work and will not like. In my experience on my own system some are lost as that about:config setting is no longer there the way it was written. It may be there under a different name/setting (good luck finding it) or it is removed. Other settings that have not changed in about:config will remain.

There is no way to tell what will be lost unless have a list of all your settings that you have made. If you do then you can install the Developers Edition https://www.mozilla.org/en-US/firefox/developer/ which has a compatibility setting at the end of the install and can run 2 versions of Firefox. You can then check your list in it.

Or if worried still can still stick in the Developers Edition to learn and to customize https://www.howtogeek.com/333110/how-to-customize-firefox-quantum-and-remove-the-white-space-around-the-title-bar/ Can make it look like 56 can do all sorts of things with UsserChrome

and you can install : Going back : unfortunately 56.0.2 and below is no longer safe to use for every day use do to secuity issues, but 52.5.0 ESR is. It will continue to get security updates until May 2018, and you can download and install it from this page: https://www.mozilla.org/en-US/firefox/organizations/all/ Note : Legacy Extensions will be deleted or removed in any version update after May 2018.

You should make a backup of your Profile before going back and just because: https://support.mozilla.org/en-US/kb/back-and-restore-information-firefox-profiles

While you transition. put name of addon in here https://mozilla.github.io/extension-finder/ find a replacement, if non they maybe still coding or someone will fill the gap.

Please let us know if this solved your issue or if need further assistance.

Quantum*Bleep* said

"My question is, will the changes we make in about:config be lost when Firefox updates?"

The Profiles is separate from the Firefox Program folder. Your settings written to prefs.js should not be affected. There have been occasions where a Preference default was changed in a new major version or update but it does not change user set preferences.

Hedge your bets: keep a backup copy of prefs.js in a safe place (i.e., a place Firefox doesn't modify).