How can the page know I'm analyzing it with firebug

detection, firebug, gmail, javascript

Solution

You can do:

if(window.console && window.console.firebug)
{
    alert("Firebug active!");
}

Problem

Look: ! Wow! How can the webpage know I'm using firebug? BTW I couldn't find out how to show the translucent add banner.

Original source