Fix for no "Add Overlay" button in newer versions of Firebug Rated 4 out of 5 stars

I've found a fix posted posted here:
https://github.com/openhouseconcept/PixelPerfect/issues/48#issuecomment-7194152

Seems to have worked fine for me. Good luck! Hopefully some day the developer will update the plugin. I saw new versions of the plugin available on GitHub, but these versions had an entirely different (and much worse, in my opinion) interface and didn't seem to function at all.

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