I think that Mozilla's strange position, being a non-profit that is at various times either in competition or in cooperation with the world's largest tech companies, makes employee departures all that more press-worthy that the typical corporate churn. I wouldn't read too much into it.
That's their mission (allegedly), but things like Pocket integrations, or the Telefonica chat thing (Hello?) really make me think it's not where the manpower is going.
Same goes for Pocket.
Meanwhile, we still don't have any FLOSS implementation for WebRTC-based voice+video.
In other words, everything is reusable and is being used by tons of new startups and projects doing video conferencing.
The whole thing will even use free codecs if both sides support it.
People moved to firefox because IE was slow and sucky. They moved to Chrome because Firefox was bloated. Now some are even moving back to Firefox because Chrome guzzles RAM. Servo would be an ideal next step; a large architectural change like that is perfect for gaining lots of traction.