But why does it have to be the case that the leadership of an opensource project have to emulate the desperation and authoritarianism of a potentially stagnant tech sector.

I don't think it's malevolence from the mozilla leadership team but more that if you hang around people who have bet their lifesaving on the success of cloud based LLMs, being cautious and making their use "optional" might begin to sound like a really controversial position even if that's actually what the users/community want from Mozilla.

Firefox market share have been declining and it's not easy to point to any obvious technical problem, so the reason for the decline is likely that the Mozilla corporation keep messing up the narrative by acting like just another Silicon Valley tech firm.