YSlow is a Firefox add-on designed to tell you why a web page is running slow based on Yahoo's rules for high performance web sites.

With the help of the YSlow  extension, you will know why web pages take so much time to load.

What's New in This Release: [ read full changelog ]

· Compatible with latest Firefox 3.6, as well as Firefox 4 Beta
· Compatible with Firebug 1.6 beta
· Updated JSLint version (2010-09-16)
· Improved error message display (removed pop-up, using console instead for error message)
· Fixed some infinite loops issues for redirects and some autorun weird behavior
· Added new rule for detecting empty src or href (, , and )
· dded logic to not consider deferred scripts on head as offenders — previous version of YSlow complains when scripts tags are inserted dynamically into the HEAD tag. Such scripts do not block page rendering and are downloaded in parallel with other resources
· Fixed inconsistency in displaying Expires date inside YSlow report Summary View column
· Fixed “JavaScript at bottom rule” issue — previous version of YSlow complains when scripts tags are inserted dynamically into the HEAD tag, now it doesn't consider dynamically injected scripts into HEAD
· Fixed issue running JSLint from a page loaded from a previous about:blank