All menu items under Grade tab can not be clicked Rated 4 out of 5 stars

I use the latest version of Firefox + Firebug + YSlow, but all menu items under YSlow Grade tab like "Add Expires headers" can not be clicked. When I use yslow 3.1.4, there is no problem like this, please fix it, thanks a lot.

This review is for a previous version of the add-on (3.1.7).