Firebug is an extension for Firefox, but what happens when you need to test your pages in Internet Explorer, Opera, and Safari? If you are using console.log() to write to Firebug's console, you'll wind up with JavaScript errors in these other browsers, and that's no fun.

The solution is Firebug Lite, a JavaScript file you can insert into your pages to simulate the Firebug console in browsers that are not named "Firefox".

Wow, now you can sanely debug AJAX in IE and Safari as well as Firefox!