JavaScript 1.7 support is available starting in Firefox 2 Beta 1, as well as in current Minefield (trunk) builds.
JavaScript 1.7 is a language update introducing several new features, in particular generators, iterators, array comprehensions,
letexpressions, and destructuring assignment. It also includes all the features of JavaScript 1.6.
For an exhaustive list, read this.
Hello again, this is Peter Gurevich, Performance PM (among other things) for IE7. We have heard a lot of requests to improve our Jscript engine, especially now that AJAX sites are becoming more prevalent on the web.  I want you all to know that we have been listening and have recently made some great fixes to our engine to improve the garbage collection routine and to reduce unbounded memory growth. You should see noticeable improvements on AJAX sites in the Release Candidate we shipped last week. I want you also to know that performance of the object model and JavaScript engine will be an area that we focus on strongly in future releases.
Read the rest here.
I found an interesting guide for (not obvious) Javascript code optimization.
Remember these quotes before reading the article:
The article is here.
This article introduces AJAX to ASP.NET developers implementing an example web page in different ways using ASP.NET Atlas, ASP.NET callbacks, Ajax.Net, Anthem.Net and MagicAjax.Net.
Last week IE Team has released a new version of IE Developer Toolbar. Althrough it’s still beta 2 (as latest), it’s a new build.
You can download it from here.
A really nice and working sample.
ZDNet.com presents an article with a list of websites using AJAX/Web 2.0 technology. Many of them are office software. I’ve tried some and I’m impressed, but most of them are in an early stage.
I tried: