Fivestar Widget Does Not Render Correctly In IE vs Firefox

Check this page in I.E. and Firefox, see how the widget displays the "half" star incorrectly. How can this be fixed. I can create a javascript to adjust the css depending ont he browser, but I have NO CLUE what needs to be changed. It is most likely a matter of increments int he width or positioning of the background image. In fact I'm alomst sure it is, but I cannot figure out how the half star is created. Could you provide a solution for this please? Thanks.