When I use firebug to watch the style of any object, I see the CSS input. For the textarea I'm writing this text into, for instance, it displays "13px/1.231 Georgia,freeserif,serif". What I want to see is the result of the rendering process, in other words the output of the rendering engine, which is not only dependent on the styles defined with the web page displayed, but also depends on the system fonts being installed, my settings in about:config and something more: I just pressed ctrl-+ what increased the displayed font size, but the element style displayed remains the same as above. I want to look elsewhere to see an increased font size in this event. Where do I have to go ?