This applies to JQuery UI 1.0 with JQuery 1.2.1 (Stable).

On line 286 of ui.slider.js:

$(this.element).triggerHandler("slidechange", [e, this.prepareCallbackObj(this.interaction)], o.change);

And on line 289 of ui.slider.js:

$(this.element).triggerHandler("slide", [e, this.prepareCallbackObj(this.interaction)], o.slide);

In both lines, the variable "e" is undefined. This is causing a fatal error in FireFox 2.0.0.11.

I suppose the solution could be to simply replace the e variable to true. This fix appears to have no side effects.