Why Is My Site So Slow? Find Out With Jiffy and YSlow for Firefox

Here are two great Firefox extensions you can use to test your site’s performance. Both operate as add-on panels to the popular Firebug extension, sort of meta-extensions if you will.

The first add-on, Jiffy, was created by Netflix user interface engineer Bill Scott. It’s basically a comprehensive timer for JavaScript events. Switch to the Jiffy panel in Firebug when you load a page, and you’ll see the timers start to run. Each JavaScript event gets its own line on a long graph, giving you a clear visual indication of which scripts are running longest. Bill built the extension on top of the Jiffy suite, a website performance measurement suite developed and maintained by the team at Whitepages.com. You can read all about Jiffy on its page at Google Code and on Bill Scott’s blog. Bill also offers a peek into how he tests the script-heavy Netflix UI.

The second speed-tester you should check out is YSlow. This add-on, which also works as an enhancement for Firebug, comes from the kind folks at Yahoo. According to the website, YSlow measures your site’s speed against Yahoo’s rules for high performance websites. It generates a little report card that analyzes your page’s events and components, pointing out which pieces of the page are causing the most problems. It also gives you advice for speeding up your downloads (“Put CSS at the top,” and “Remove duplicate scripts”).

Both handy tools, both built off of Firebug. Which forces us to ask: What ever happened to Chris Pederick’s Web Developer add-on? A year ago, it was the must-have tool for analyzing pages, but now Firebug has greater traction with developers, and is suddenly capable of so much more. With over 7 million downloads, loads of people are obviously still using it, but what does the future have in store for Web Developer?

Also, be sure to check out the Webmonkey Stopwatch for simple site speed testing!