Angus Croll covers the new 'use strict' operator introduces in EcmaScript 5th edition and how to get started using it. He offers a set of unit test to see how well supported strict mode is in your browser.
JavaScript documentation surrounding version 1.5, 1.6 (supported by Firefox 1.5 and Mozilla 1.8), and version 1.7 (supported by Firefox 2.0). Backed up by mailing lists, newsgroups and an IRC channel