I tried to make the change manually in both Settings and about:config.
Change was from "Use System Handler" to /home/[USER]/.mozilla/firefox/[XXX].default-release/favicons.sqlite
At the top of the Settings page is the line "Your browser is being managed by your organization".
Didn't get any errors, but the change was not saved in either environment.
Instead, it retained value of Use System Handler.
