Autocomplete item list .5px shift

Autocomplete item list .5px shift

I'm using the autocomplete on a page of mine and when you type the first letter in it brings up the list and it has a left position of xxx.5px type next letter and it drops to xxxpx then next letter its back to xxx.5px this happens with each letter press this is with just using the base style from the main download. This only happens in firefox as well. So i haven't added any styles to it except for the ones provided. And no extra js either. Any ideas?

Thanks.