A few weeks back we’ve already posted about YSlow, a free plugin from Yahoo that works on top of Firebug that additionally computes a performance grade report for your website.

A new version has now been released: YSlow v0.9.3, and one of it’s notable new features is that it works now on Firefox 3 beta3 and later. For those that didn’t try Firefox 3 yet, we can already say it improves rendering speed and uses a lot less memory then Firefox 2. Unfortunately not all the plugins have been made compatible yet with Firefox 3, so you may want to wait a bit before removing Firefox 2.

As a webdeveloper you’re probably already using the fantastic Firefox plugin Firebug. Features like inline editing of HTML, CSS, DOM inspection and HTTP requests viewer makes your developer life infinitely easier.

YSlow, a free plugin from Yahoo that works on top of Firebug additionally computes a performance grade report for your website.

Some of the rules it uses are:

1. Make Fewer HTTP Requests
2. Use a Content Delivery Network
3. Add an Expires Header
4. Gzip Components
5. Put CSS at the Top
6. Move Scripts to the Bottom
7. Avoid CSS Expressions
8. Make JavaScript and CSS External
9. Reduce DNS Lookups
10. Minify JavaScript
11. Avoid Redirects
12. Remove Duplicate Scripts
13. Configure ETags

Implementing these performance improvements suggestions may speed-up your site greatly as according to Yahoo’s research almost 80% of the time is spent on the client side. So optimizing your Java server side code is not the only thing you should be focusing on 🙂

YSlow 0.9 improves the plugin for Web2.0 applications as it now supports AJAX requests, frames and iframes. There are several other new features and bug fixes described in the release notes including highlighting HTTP 404s, better detection of CSS expressions and JavaScript minification, and searching within the YSlow panel.