How to enhance ItemSelector scrolling performance?

I'm using an ItemSelector with two lists like the second one from this demo:

http://dev.sencha.com/deploy/dev/examples/multiselect/multiselect-demo.html

I ha开发者_StackOverflow中文版ve around 600 items in my first list and the performance when I drag the scrollbars is unacceptable in Firefox 3.x. For some reason, IE7 is not a problem. Are there any optimizations than can be done so scrolling will be faster?

[Update]

Seems like the problem occurs when the widget is placed in a xtype: 'fieldset'

The problem goes away once the widget is moved out of the fieldset.

did you try disabling firebug ?

In the demo I can't see any events firing on scrolling up and down.

Possibly you have some set up in yours.

You could possibly override the renderer of the list to use fewer elements, it's currently three per item. Not holding out a huge amount of hope on that front however.

Your best solution is likely to find a way to not have 600 items displayed on the page at a time.