It's on the next line in Firefox on the mac also.
You can't just add some px to the end of some text content and expect it to be the same cross browser as all render it differently by as much as 10px for the whole line in some cases (not counting users who large text settings or have 120dpi settings and large fonts etc).
Remove the left and right empty list elements and as you never want to do things like that.
Add a red background to the ul and a black background to the list element. Then give the UL some left padding and then clear the floats.
padding:0 0 0 200px;
That leaves breathing space on the right to soak up the differences.