Bug and feature ask Rated 4 out of 5 stars

I found a bug.
When firebug has one of another addons as yslow,firecookies, eventsbug (I don't know exactly what addon), then if I click on pixel perfect tab, then it doesn't open.

And also, can you add 1 feature of centering of the testing image?

This review is for a previous version of the add-on (1.5.6).