[jQuery] slow and jerky slide on Firefox 2.0.0.13 (Ubuntu/ Core-2 : 1.8GHz)

[jQuery] slow and jerky slide on Firefox 2.0.0.13 (Ubuntu/ Core-2 : 1.8GHz)


Hi,
I started using Jquery 1.2.3 (uncompressed) for development and
learning/.
Just one simple effect in whole page using the Jquery tutorials, a div
is toggled (slideUp/slideDown) when a button's is click.
This runs smoothly on Opera (Ubuntu), but very sluggish on Firefox
(Ubuntu). For sake of precaution initially firebug, and at last all
the Addons in Firefox were uninstalled. Still the performance is same
unchanged.
Here is the code:
$(document).ready(function(){
    var $box = $('#userPanel');
$('#UserPanelButton').click(function() {
    $box.blindToggle(500);
});
    $box.blindToggle(500); // To show the animations automatically on-
load
});
jQuery.fn.blindToggle = function(speed, easing, callback) {
var h = this.height() + parseInt(this.css('paddingTop')) +
parseInt(this.css('paddingBottom'));
return this.animate({marginTop: parseInt(this.css('marginTop')) <
0 ? 0 : -h}, speed, easing, callback);
};
------------
Please guide me where is the problem?