Y!Slow

Some background -

http://ajax.phpmagazine.net/2007/07/yslow_helps_you_speed_up_your.html
http://developer.yahoo.net/blog/archives/2007/07/yslow_release_o.html
http://www.phpied.com/yslow-performance-extension-for-firebug/
http://corfield.org/blog/index.cfm/do/blog.entry/entry/Improving_site_performance_with_YSlow

Firebug -

http://www.getfirebug.com/

Firebug integrates with Firefox to put a wealth of web development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.

YSlow -

http://developer.yahoo.com/yslow/

YSlow analyzes web pages and tells you why they’re slow based on the rules for high performance web sites. YSlow is a Firefox add-on integrated with the popular Firebug web development tool. YSlow gives you:

Performance report card
HTTP/HTML summary
List of components in the page
Tools including JSLint

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Professional 2.0 .NET is intended to get the like minded professionals using Web 2.0 tools in their profession to manage and work efficiently.