Rated 3 out of 5 stars

Great add-on. I only have one request. It would be great if one could isolate the CSS to a selected region within the page. For example I would like to see just the CSS rules of a nested div and all of it's containing elements (unlink firebug which only shows the CSS rules for the selected element only), including all the inherited rules and without any of the rules used for other regions of the page. In other words, I want to get all of the styles for a form or a table, etc. within a page but no other rules used on the page such as those used for the surrounding paragraphs, lists, etc.

This review is for a previous version of the add-on (0.1.7). 

Unlikely

Seems to me like that would be more appropriate for Firebug than for "CSS Usage".