[toomuchtodo]

You should only be in a position long enough to a) learn enough to move up to the next position or b) effect the change you want to if you're C-Level.

If you're not learning anymore, it's not fun anymore, or you're not having the effect you want to (or any combination of those), its time to leave.

[Manishearth]

This. I think most Mozilla employees approach stuff this way. I've seen folks leave to form a startup other times too, and that's not because Mozilla is bad at keeping them.

I (non employee; student+volunteer) certainly do this. I've drifted between open source projects and communities, reducing participation drastically when I find something I learn from more. Im pretty involved in a couple projects and I really want to stay because they're awesome, but it's quite possible that in a few years I'll be somewhere completely different. At the moment, I hope not. But only time will tell.

[GuiA]

Yeah, you're not disagreeing with what I just said. If he couldn't effect the change he wanted to as CTO, then Mozilla is probably in a very poor position.