Firebug Console Stopped Working and I Fixed It

Somewhere along my way, I lost my ability to use Firebug console, specifically, I could not use console.log(). Worse, I could not examine variables and DOM elements from the console. It would echo the thing I typed but not the result. For example, if I typed "5+5" into the console, the result should look like:

     

While broken, it only showed the ">>> 5+%".

I tracked it down to a jquery statement:

     $('body').html("<div id='container'></div>");

When I changed it to:

     $('body').append("<div id='expressbook'></div>");

It worked correctly.

Someone please explain.