Question

What’s a surefire way of detecting whether a user has Firebug enabled?

Answer 1

Original answer:

Check for the console object (created only with Firebug), like such:

if (window.console && window.console.firebug) {   //Firebug is enabled } 

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Update (January 2012):

The Firebug developers have decided to remove window.console.firebug. You can still detect the presence of Firebug by duck typing like

if (window.console && (window.console.firebug || window.console.exception)) {   //Firebug is enabled } 

or various other approaches like

if (document.getUserData('firebug-Token')) ... if (console.log.toString().indexOf('apply') != -1) ... if (typeof console.assert(1) == 'string') ... 

but in general, there should be no need to actually do so.