I use Firefox and I always see the stars. I have seen it used with vbuletin. It is a thread rating tool that readers can rate the thread. It shows only in the menu bar on threads first post. It is a drop down menu called "Rate this thread"
With a star rating from "Excellent to Terrible" in five steps.
I do not think it is browser dependent.
And I have given this thread a 5 star rating!
For the ones that do not see the stars, I have not a clue why?