> maybe it is also because their ressources are limited and implementing a new language like dart is somewhat expensive. And NaCL even more I think.
If I recall correctly, Google offered to donate their engineers' time to implement Dart and/or NaCl in Firefox and Mozilla still refused.
Also, WebAssembly is enormously more complex to implement than NaCl.
And, both of these events occurred while Mozilla was napalming skyscraperfuls of $100 bills with their Firefox OS nonsense.
BTW, of the things I mentioned the only ones I'm really "angry" at Mozilla for are WebSQL and NaCl, the others I can see both sides.