This is just my speculation, as a mere Firefox user with no insight into Mozilla's larger strategy or financials, but it kind of feels like Mozilla is stuck in a Google-funded local optimum. Maybe this shake-up can provide the activation energy needed to break out into something better?
Mozilla will lose 86 percent of its funding if the Google deal goes away. Unless they can somehow generate an equal amount there will be massive layoffs and Firefox will be in a death knell. So far they have not managed to wean themselves off the Google money.