Javascript popup triggers browser quirks mode

Question

I have a simple javascript snippet to show a popup with a textArea and a button inside:

var popup = open("", "Popup", "width=400,height=400,top=250,left=550");
var area = popup.document.createElement("textarea"); 
var but = popup.document.createElement("button"); 
popup.document.body.appendChild(area); 
popup.document.body.appendChild(but); 

if I use it in browser console it works fine, as expected. I'm trying to make a clickable bookmark on my bookmarks bar (Firefox) but if i put these few lines in a bookmark (setting as bookmark url Javascript: var popup = open.... ) then I'm facing some problems, while the popup still appears as expected, the main browser page turns blank with only [object HTMLButtonElement] written in the upper left corner, then looking at the browser console there is a warning about quirks mode enabled. Why is it so?