After some digging it was really quite simple …
if(window.console && window.console.firebug)
{
alert("you are using firebug");
}
Try it out for yourself by clicking the following link: Is Firebug running?
Some people have a problem with this but it’s a proactive way for them to make their email be more responsive… I can’t live without Firebug, because it’s a great tool, BUT I keep Firebug disabled most of the time because it slows my browsing experience.
Cool !