I previously used stylus ff extension, but I really loved Stylebot when you quickly need to edit few DIV elements or Hide AD banners. Its good even for people who dont code in CSS. Im still not sure how to use the Readability option, but non the less I like this extension.

amazing product

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This extension is the perfect solution for editing and saving the edited CSS styles of any visited webpage. It is easy to use. It allows to edit styles with help of forms or manually edit the CSS code. And after that, the rules are saved and applied to the edited webpage each time it is loaded.