sIFR calculates the dimensions of the element you're applying it to. Floated elements are shrinkwrapped and take up only the width in which its necessary for the text inside to display.
I suggest you give an id to each of those lis, something like
li#nav-blog { width:200px; }
This will give you finer control over how much area each of those nav list elements take up, and more space for sIFR to use.
meder
2009-08-23 01:23:14