How to make a Firefox Extension URL Button show a string when hovered over

Question

I have made my full FF extension, and there is a button in the URL bar. The boss now wants the button to show a certain string when you hover over it. Here is my current cod

Answer 1

Awwwww man all that work for nothing. The attribute is not tooltip but it is tooltiptext! So just do btn.setAttribute('tooltiptext', 'what ever you want');

var loadURLButton = function(doc, urlBtnClick) {
    var urlBarIcons = doc.getElementById('urlbar-icons')
    var btn = doc.createElement('toolbarbutton');
    btn.setAttribute('id', 'urlbutton');
    btn.setAttribute('tooltiptext', 'mytt');
    btn.setAttribute('image', 'chrome://branding/content/icon32.png');
    btn.addEventListener('command', urlBtnClick, false);
    urlBarIcons.appendChild(btn);
    return btn;
}

var doc = document;

var urlbarButton = loadURLButton(doc, null);