Mike Schroepfer, Mozilla's vice president of Engineering, has left Mozilla to join Facebook as its director of Engineering. I only met Mike once but was hugely impressed by him. His loss, while it shouldn't significantly hurt Mozilla's continued momentum, is a loss to Mozilla.
That's the problem with being a non-profit. It will always be hard to retain people long-term since there's no possible pay-out at the end. Mozilla has done an exceptional job of hiring great people, but I worry that it (along with Eclipse, Linux Foundation, etc.) will be able to keep those great people for the long haul.
I personally believe that the non-profit foundations may hold the future to building the next generation of exceptional open-source software. It would be awesome to see those that have made significant money in open source take a turn within these non-profits, lending their perspective and expertise.
As for Facebook, it scored big in recruiting Mike. This speaks well of Facebook's commitment to open source and the open web. Mike wouldn't have joined without feeling that Facebook would be contributing to the work he's been doing at Mozilla. He has a history of calling out pseudo-open source when he sees it.