If you want to fiddle around with a web page in Firebug, or any other Javascript inspector, it helps to have jQuery loaded. If you search online there are bunch of weird ways listed, but this is the one I found that consistently works:
var s=document.createElement('script');
s.setAttribute('src','https://ajax.googleapis.com/ajax/libs/jquery/1.6.4/jquery.js');
document.getElementsByTagName('body')[0].appendChild(s);
It will load jQuery from a secure (HTTPS) url, and inject it into the body tag.
It’s also available as a bookmarklet (just drag to the top) : Load jQuery