It is possible to unlock about:config preferences in Firefox forks. This is done at the installation level, so it is not customizable per-profile. I will be using Zen Browser as my example here, but this works in other Firefox forks as well.

First, navigate to your installation directory (e.g., C:\Program Files\Zen Browser). In this directory, create a text file and give it the .cfg extension. In this example, I've named mine zen.cfg. Type // on thee first line, then for each pref to unlock, add a line with "unlockPref("example.prefname");", replacing example.prefname with the name of the preference you'd like to unlock. If you'd like to set a default value for that preference, you may do so by adding a line with defaultPref("example.prefname", value);, replacing value with your desired default value. You may use // at the beginning of a line if you'd line to add comments

Here's my example for unlocking URLbar suggestion preferences in Zen Browser:

// SKIP THIS FIRST LINE
unlockPref("browser.urlbar.suggest.topsites");
defaultPref("browser.urlbar.suggest.topsites", false);
unlockPref("browser.urlbar.suggest.quicksuggest.nonsponsored");
defaultPref("browser.urlbar.suggest.quicksuggest.nonsponsored", false);
unlockPref("browser.urlbar.suggest.quicksuggest.sponsored");
defaultPref("browser.urlbar.suggest.quicksuggest.sponsored", false);

Next, you'll need to /defaults/pref inside the installation directory and create autoconfig.js, with the following contents:

pref("general.config.filename", "zen.cfg");
pref("general.config.obscure_value", 0);

Replace zen.cfg with the name of your .cfg file from before (or leave it as zen.cfg if you use mine).

Restart your browser and go to about:config to see the newly-unlocked preferences.