css3 transitions not firing first time in Firefox 4

I am experimenting with some css3 transitions. I put together a quick slider test and it works well in the webkit family. In Firefox 4, the first time you click on the left link the slider is suppose to slide to the left, however, there is no css transition until the second time you click the link. I put the demo up on jsfiddle - http://jsfiddle.net/mrleroylee/ctY68/

Is this a result of something in my code or开发者_JAVA百科 is this a bug?

Set left: 0 in your styles for ul; that got it working in the fiddle for me: http://jsfiddle.net/ctY68/4/

Looks like Gecko isn't considering your first style change a transition because there was no initial value set.