When you run:
window.toString.call(\"\")
everything\'s fine in FF/CH but in IE8 you get a script error. Investigating a bit more it turned
NickFitz is correct, the toString method on the host object that you are finding is purely so that if you did
alert(window);
you would get the text [object]
All that the javascript method toString() used in your examples would acheive is to make a string from a string so the correct way to do what you are trying is;
var a =new String ("");
or simply
var b = "";
or if you really want to be silly;
var b = "".toString();