Good addon Rated 4 out of 5 stars

Need more functionality for css:
After I push button "CSS" and go to css editor. I need to know here is it workable rule or not. It would be better mark working rules and not working. (1)
When I edit one of the rule it would be better if I have options for show me that elements on page. All of them. For example I am edit "a" selector options. Let's FireBug highlight all "a" on the page. (2)
It would be better if FireBug can work like a Stylish - for edit and load css local until new design will be approved. But better here realize 2 things - save css in independent css files (not like Stylish in one sqlite database).(3.1) 2nd - have options for absolutely priority under all styles on site. Even "*" selector should have more priority then "#" from the site. It can be switchable options.(3.2)

This review is for a previous version of the add-on (1.9.1).