Rated 4 out of 5 stars

Works great with FF8 with this new version. Very happy.

If it would work when FireBug is in the pop-out mode then it would be a 5/5 plugin

This review is for a previous version of the add-on (1.7.1). 

Barely Works Rated 1 out of 5 stars

The plugin works, but only if you have FF 3.6. But even in FF 3.6, it only just barely works. If you undock FireBug, Pixel Perfect Becomes completely useless. You become unable to change any settings or add/remove the overlay to the page.
This plugin has a lot of potential to be great but is currently useless in FF 4, 5, and 6

This review is for a previous version of the add-on (1.6.1).