This extension includes a toolbar which includes special tools for web developers, because hey are focused on web design.
Thanks to Web developer we will be able to see the source code of any website, access the CSS, info about the domain, and a large etc.
Furthermore, it includes code validation features and options for activating/deactivating web elements. It also allows you to change the CSS and see the transformations in real time.
All this, from a tiny bar which will not annoy your surfing experience and which will let you work faster.