I'm not sure if you responded to the wrong comment, but the gpp was suggesting building it in by default.

If Firefox included it by default then it would remove a layer of deniability.

What do they need to deny? Ad blocking is clearly a feature many users want. It’s often the only extension people install. If I were Firefox, I’d build it right into the core of the engine. Turn it on with a checkbox and/or custom blocklist sources.