If they pivot towards "mainstream appeal", it usually comes to the expense of that user community. Their alternative is to be the best Firefox they can possibly be, and wait for users to join their audience organically.

It feels like Vivaldi has done a better job of sticking to a clear user persona model. They are clearly targeting power users and Opera 12 refugees, and it feels like that still informs what they do. Unfortunately, the one thing they can't do is make a browser that doesn't run like cold treacle.