window.getSelection() of textarea not working in firefox?

I am trying to get selection text on HTML page.

I use below code, and window.getSelection() on textarea seams not work in firefox, but works fine in Google Chrome.

• I am using firefox 24, and chrome 27.

Here is a sample: http://jsfiddle.net/AVLCY/

HTML:

<div>Text in div</div>
<textarea>Hello textarea</textarea>
<div id='debug'></div>

JS:

$(document).on('mouseup','body',function(){
   $("#debug").html("You select '" + getSelectionText() + "'");
});

function getSelectionText() {
    if (window.getSelection) {
        try {
            // return "" in firefox
            return window.getSelection().toString();
        } catch (e) {
            console.log('Cant get selection text')
        }
    } 
    // For IE
    if (document.selection && document.selection.type != "Control") {
        return document.selection.createRange().text;
    }
}