Had an interesting message come up while using Gmail - Disable firebug: The logging of the Ajax calls seems to be slowing Gmail down according to Google, not that I have noticed any performance issues. The interesting thing to me is, how do they know I am using Firebug? I looked at Firefox's user agent via javascript and didn't see anything there that indicated I was using Firebug. I took a quick look at Gmail's obfuscated js code and searched for the message, but didn't find anything. Not that it matters, but I wonder how they know I have Firebug installed and enabled?