Is there Firefox addon to identify performance problems in web applications?

"Check out Yahoo's YSlow, it works in combination with the Firebug Firefox addon.

YSlow analyzes web pages and suggests
ways to improve their performance
based on a set of rules for high
performance web pages. YSlow is a
Firefox add-on integrated with the
Firebug web development tool. YSlow
grades web page based on one of three
predefined ruleset or a user-defined
ruleset. It offers suggestions for
improving the page's performance,
summarizes the page's components,
displays statistics about the page,
and provides tools for performance
analysis, including Smush.it™ and
JSLint.

Another option is the Charles web debugging proxy. It's a very useful tool for web application development in general (both javascript and flash), and one of the features is a chart showing all the objects/requests loaded, and the time they take."

There is the new Speed Tracer by Google.