YSlow for Firefox
Optimizing your web site is one of the most important factors when constructing your awesome web site, but designers are always looking for the best way to make your web site scream.
I know what you're thinking. Why are you talking about Firebug when this review is about YSlow? Because the Yahoo! Developer network created a Firefox add-on to a Firefox add-on. They built another tab in Firebug called YSlow, which is their web page analyzer.
First, you need to install Firebug. After installing Firebug, install YSlow. The extension is transparent until you actually need it, just like Firebug. Press F12 to toggle Firebug and you should instantly see the new tab called YSlow.
Of course, a new tab is added to Firebug along with the additional pulldown menu options.
The Performance option reloads your current page and analyzes it for any ideas on how to improve your web page. YSlow proceeds to list all of the issues that need resolved on the page. After running YSlow on DCS Media, some of the issues listed are completely unavoidable, like the amount of external CSS files used for the site or the "Avoid CSS Expressions" item, which is IE specific. Even though they were reported, there are currently only two CSS files used on the site. Not quite what I consider "excess files."
The Stats option provides a summary of what the page contains, how long it took to load, cookies you picked up from the page, and the amount of objects in an empty cache and full cache.
Since YSlow attaches to Firebug, there aren't any options for this add-on. The options button is even disabled in the Add-ons dialog box. I guess that's that.
Based on what I've seen from Yahoo! Exceptional Performance Group (does that make them the YEP Group?), this add-on is an awesome add-on and rightly deserves a 5 out of 5 rating.
UPDATE: Coding Horror has an update as to the scoring of Yahoo's YSlow extension. Quite enlightening.