This is a quick list of Add-ons in FF that I use:
- Firebug - http://getfirebug.com/
- IE Tab - https://addons.mozilla.org/en-US/firefox/addon/1419
- MeasureIt -http://www.kevinfreitas.net/extensions/measureit/
- ColorZilla - http://www.colorzilla.com/firefox/
- Resizeable textarea - https://addons.mozilla.org/en-US/firefox/addon/3818
- Web Developer - http://chrispederick.com/work/web-developer/
- HTML Validator - http://users.skynet.be/mgueury/mozilla/
- CSS Validator - http://www.nu22.com/firefox/cssvalidator/
- Operator - http://www.kaply.com/weblog/operator/
- Tails Export - https://addons.mozilla.org/en-US/firefox/addon/2240?id=2240
- ShowIP - http://code.google.com/p/firefox-showip/
- YSlow - http://developer.yahoo.com/yslow/