If you computer is open to anyone use it then anyone can delete or remove what they want. What your asking is a Windows password change so any changes need Admin password to make those change. This falls outside of firefox End User support and is a Windows control panel issue where you need to create a admin/owner password and a stand account so that without the password people can't just remove and add things they want. Don't know if this will extent to the Browser addons but it could and this would stop people user from doing what they shouldn't do. So in the end this is a Windows O/S control issue permission privileges and not some directly tied to the Browser itself persay.

You can consider to use policies to lock extensions.

• https://support.mozilla.org/en-US/kb/customizing-firefox-using-policiesjson

• https://github.com/mozilla/policy-templates/blob/master/README.md
• https://github.com/mozilla/policy-templates/blob/master/README.md#extensions-machine-only
• https://github.com/mozilla/policy-templates/releases