There are no settings that could be password-protected. It is forbidden by Mozilla to keep users from uninstalling extensions. You could have a look at https://github.com/serv-inc/blacklist/blob/master/example_policies.json which is a file to automatically install and keep from uninstalling inside the browser. Usage should be similar to https://github.com/serv-inc/safe-search/wiki/Bulletproof-installation. Any questions, feel welcome (best raise an issue at github) If this is fixed, changing the rating would be welcome.

Thank you for the feedback. Could you write which sites failed for you? Best use https://github.com/serv-inc/blacklist/issues.

UPDATE: yes, many of even the top 10 sites were not in the blacklist. Some have been added at https://dsi.ut-capitole.fr/cgi-bin/squidguard_modify.cgi. Add more to improve the list and this addon.

UPDATE: Have a look at version 0.5. Still, reporting any missing files via the link above (or Email to the list's curator fabrice.prigent@ut-capitole.fr) would be appreciated.

Finally, Firefox can be configured for addons. See https://github.com/mozilla/policy-templates/blob/master/README.md for how to do this and https://github.com/serv-inc/blacklist/blob/master/example_policies.json for basic usage. (This blocks deactivation and removal, at least on a fresh FF install).

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Thanks for the suggestion. To disable all addon removal, have a look at https://addons.mozilla.org/en-US/firefox/addon/block-about-addons/. (If you install this, there is still one way to disable all addons at once, but that seems impossible to prevent. Firefox 60 and ESR 62 also provide some security: https://blog.mozilla.org/futurereleases/2018/01/11/announcing-esr60-policy-engine)

Yes, it's a huge list, even reduced to the top million. ;-))
But, alas, the honor is not mine. ;-))
It's due to the fine admins of http://dsi.ut-capitole.fr/blacklists/index_en.php . ;-))