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: 
I was wondering this myself recently. Obviously the DHTML doesn't make sense, but the basic syntactic sugar and things are rumored to work.

* There is this [jQuery on XUL](http://groups.google.com/group/jquery-dev/browse_thread/thread/4545040bf26c6eea?pli=1) discussion from the jQuery group which indicates that it loads up with some exceptions.
* Also see this slightly more recent blog post about [jQuery and DHTML in XUL](http://digitalmihailo.blogspot.com/2008/05/jquery-and-dynamic-html-in-xul.html). That person is going after the HTML within the XUL which is not exactly what you need but he does have good information.
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