I use ESR with pre-baked policy[0] stored in /usr/lib/firefox/distribution/policies.json before the installation/1st run. Configures cookies, studies, disables logins, credit cards saving, asking for location, promptimg for notifications, studies, pocket, telemetry etc. During 1st run, it installs all pre-defined extensions.

For some reason, changing search engine via policy no longer works, but that can be bypassed by auto-installed extension that changes search engine.

[0] https://mozilla.github.io/policy-templates/