No, because while JavaScript is the "common" language of the web, its not the only language you can code in on the web -- there are plenty of implementations of other languages with it as a compilation target.
The value of having a guaranteed-to-be-everywhere target language for the web, even if it isn't the preferred development language of every developer, are fairly obvious.
> Mozilla's mission to protect the web from all languages but Javascript is locking us into a future where there will be no choice and nothing better than Javascript
As long as JavaScript keeps getting better -- and, particularly, as long as it is spurred on in that by efforts which propose alternative standard languages for the web with compelling stories so that JS has to keep moving forward in order to be acceptable as the universal, guaranteed target language -- that's fine. "Nothing better than JavaScript" isn't a real limitation if JavaScript is a moving target.