Putting the flags in Firefox just seems logical not "Hostile Design". Yes, there could be an easier way to turn it off, such as a menu item, but the flags need to be there first before the menu entry can exist.
The author claims to be an "IaaS engineer", surely, he can figure out how to write a firefox plugin, that can do what he wants, and use that to help non-technical users, and if it becomes popular enough will probably effect the change he wishes to see.
Why can't the menu entry be created alongside the flags? Surely if it's too complicated, then creating a plugin would also be too complicated for someone who doesn't work at Mozilla and doesn't know the codebase?
Its not just that each new "feature" is unnecessarily difficult to disable, and already active-with-privacy-side-effect by the time you notice.
Most new "features" are by now covered by an existing setting and/or policy. Yet I recognize a pattern of introducing new "but did you opt out of THIS NEW thing?" or "but did you opt out of VERSION TWO of this previously rejected thing?" setting/policy. It has become unsafe to upgrade to new Firefox releases, because each one will disrespect previous user choice in another unexpected way.