- FF: Firebug : https://addons.mozilla.org/en-US/firefox/addon/1843
- IE: DebugBar : http://www.debugbar.com/
- SF: Developer: http://developer.apple.com/internet/safari/faq.html#anchor14
Debug in production?! .. when you have to .. you can target a strange userAgent string .. such as "Quality Assurance Browser" .. that you set yourself with some tool that allows you to set your userAgent.
