Your green-colored id says you are new here, and yet unwilling to do basic research in HN on the topic you ask about. I'll take this in the "Dear LazyWeb" spirit, assume that you are not trolling, and give some links. First, one of a few obvious searches:

https://www.google.com/search?q=site:news.ycombinator.com+pn...

From the results, an entry point into a deep thread, posted by Maciej Stachowiak of Apple:

https://news.ycombinator.com/item?id=4648045

Further in this sub-thread, I comment on the loaded language used to open-wash NaCl and portray critics of it as haters:

https://news.ycombinator.com/item?id=4650689

Back to your comment: "It's based on open source tools" is true of Emscripten too.

The bit about "can be easily integrated into any browser" is false due to Pepper, the large new target runtime for *NaCl. Pepper is a non-standard and unspecified-except-by-C++-source plugin API abstracting over both the OS and WebKit -- now Blink -- internals.

To make such an airy assertion in an under-researched comment makes me suspect that you don't know that much about either PNaCl or "any browser". So why did you make that confident-sounding claim?

These days, large apps are written in JS, even by hand. GWT is not growing much from what I can tell, compared to its salad days. Closure is used the most within Google, and Dart has yet to replace Google's use of GWT + Closure.

Outside Google, hundreds of languages compile to JS (http://altjs.org/). CoffeeScript is doing well still. TypeScript is Microsoft's answer to Dart, and more intentionally aligned with the evolving JS standard.

"Does Mozilla has any plans to improve the situation here?"

Have you heard of ES4? Mozillans including yours truly poured years into it, based on the belief that programming-in-the-large required features going back to "JS2" in 1999 (designed by Waldemar Horwat), such as classes with fixed fields and bound methods, packages, etc.

Some of the particulars in ES4 didn't pan out (but could have been fixed with enough time and work). Others are very much like equivalent bits of Dart. One troublesome idea, namespaces (after Common Lisp symbol packages) could not be rescued.

But ES4 failed, in part due to objections from Microsofties (one now at Mozilla) and Googlers. In a Microsoft Channel 9 interview with Lars Bak and Anders Hejlsberg, Lars and Anders both professed to like the direction of ES4 and wondered why it failed. _Quel_ irony!

As always, Mozilla's plans to improve the situation involve building consensus on championed designs by one or two people, in the standards bodies, and prototyping as we specify. This is bearing fruit in ES6 and the rest of the "Harmony era" editions (ES7 is being strawman spec'ed too now; both versions have partial prototypes under way).

Founding Harmony email (on the demise of ES4):

https://mail.mozilla.org/pipermail/es-discuss/2008-August/00...

A talk I gave last fall on ES6 and beyond.

http://brendaneich.github.io/Strange-Loop-2012/#/

For programming in the large, ES6 offers modules, classes, let, const, maps, sets, weak-maps, and many smaller affordances. I hope this helps. Even more is possible, if only the browser vendors and others invested in JS choose to keep working on evolving the language.