I've been reading up on Mozilla's continuing development of JavaScript, up through version 1.8.5: https://developer.mozilla.org/en/JavaScript.
My question is: What is the correlation between JavaScript 1.8.5+ and ECMAScript 5+ in terms of language features? Any chance Mozilla's new JavaScript features (like generators, array comprehensions, etc.) will become part of ECMAScript?
I just want to get a handle on whether it's worth learning JavaScript 1.8.5 features (and working to shim them into non-supporting browsers) or whether I should forget JS 1.8.5 and focus on learning/shimming the new ECMAScript 5 features.
FYI: Mozilla talks about how they're planning to bring JavaScript into compliance with ECMAScript 5 here: https://developer.mozilla.org/En/JavaScript/ECMAScript_5_support_in_Mozilla
JavaScript 1.8.5 is Mozilla's implementation of ECMAScript with added features. It's a superset of the ECMAScript specification (and of current implementations like IE, Chrome and Opera). Mozilla pushes for the features it adds to its own browser, they may or may not make it into ECMA. Note that Mozilla is a member of the W3C and has some say, but my guess is that most features won't make it.
Bottom Line Don't use it unless you're coding something specific to firefox, FF extensions, XUL apps, Rhino (Added Rhino thanks to @Raynos)