I don't know about the other browsers, but Mozilla's plans are here: https://developer.mozilla.org/En/JavaScript/ECMAScript_5_support_in_Mozilla https://develop

I don't know about the other browsers, but Mozilla's plans are here: https://developer.mozilla.org/En/JavaScript/ECMAScript_5_support_in_Mozilla https://developer.mozilla.org/En/JavaScript/ECMAScript_5_sup... In summary, some Mozilla JS extensions from Firefox 3.0 have been adopted into ECMAScript. Some ECMAScript 5 APIs have been added to Firefox 3.5, but not all of them. All the browser vendors have put a lot of effort into ECMAScript 5, so I'd expect they're willing to actually implement it, too.