How does this look like?
o[""]()
A bit like a syntax error, eh? Or an emoticon of some sort. Well, it's valid JavaScript code.
JavaScript objects can have an empty string as a name for a property/method. So if you create an unnamed method called "", you can't call it using the dot notation, but you can, using the brackets.
So type this in your Firebug console:
var o = { "": function(){ console.log('here') } }
then call the unnamed like o[""]()
It works!
Reminds me of the Wizard of Earthsea a little bit where you had to know the true names of things in order to do the wizardry.