Use the Page Inspector to examine and modify the HTML and CSS of a page.
You can examine pages loaded in the local copy of Firefox or in a remote target such as a Firefox OS device or Firefox for Android. See remote debugging to learn how to connect the developer tools to a remote target.
User Interface Tour
To find your way around the Inspector, here's a quick tour of the UI.
To find out what you can do with the Inspector, see the following how to guides: