Debugging a javascript error that only occurs on the live site

Something broke and I get "Object Expected" error on my live site, but I can't figure out where. If I run visual studio at the same time,开发者_运维百科 it breakpoints it and shows the error as being half way along the viewstate, highlighted yellow... which is useless as its just gobbledegook.

How can I debug this? I want to know what javascript its trying to run that is breaking it.

Firefox and Firebug.

http://getfirebug.com/

Never debug Javascript without it.

Check out ScriptCanary.com so you can get all the details from live site errors and vastly improve your chances of quickly fixing them.