Question: I know its possible to integrate jQuery within Firefox addons, but are we able to manipulate (animate, move, adjust transparency, etc) XUL elements themselves?

From what I understand, the Firefox addon can use jQuery to manipulate HTML/DOM elements, but not sure about XUL elements.

Answer: 
My explanation refers to jQuery 1.7.1.

My goal was to perform a fade animation within the XUL context, but errors were being thrown because jQuery wrongly assumes it is dealing with IE if jQuery.support.opacity is falsy.

The logic that populates the **support** Object was prematurely returning an empty Object due to the inability to interact with a DOM element created via **document.createElement( "div" )**. My problem was solved by using **document.createElementNS**:

```
createElementNS("http://www.w3.org/1999/xhtml", "div");

```

I searched the jQuery bug tracker after coming up with this solution and found the following related ticket: <http://bugs.jquery.com/ticket/5206>

jQuery isn't advertised as working within the XUL context and therefore the team has no plans of addressing the issue, though they should address the issue of the IE false positive. I am content with manually making this one line change in the source code for my application.

Cheers,
Andy
Unfortunately, jQuery fails to initialize in XUL because of the HTML-specific functions like `document.body` that exist for HTML pages only. However there is a special branch called [jQuery-xul](https://github.com/ilyakharlamov/jquery-xul) that it optimized for use in FireFox extensions. I have checked, it works fine.