Browser Add ons for webmasters.

I only use Google Chrome and Firefox. I have long sessions on the internet and firefox seems to slow down and take alot of resources, as well as crashing. Google chrome seems to be alot faster and hasn't crashed yet.

SEO Quake   (available with google chrome and firefox)

http://www.seoquake.com/

Firebug

Inspect html and elements.

http://getfirebug.com/

SEO Doctor

https://addons.mozilla.org/en-US/firefox/addon/102178/

Page Speed Test

http://code.google.com/speed/page-speed/

Live HTTP Headers

https://addons.mozilla.org/en-US/firefox/addon/3829